No.
In medicine, you always have to distinguish between a cause and a risk factor. When you fall off your bike and break your arm, then the fall was the cause, as it led directly to the injury. SARS-CoV-2, the virus, is the cause for Covid 19, the illness.

Smoking, however, is a risk factor. Take lung cancer: non-smokers can absolutely contract it, but it is actually quite a rare disease for them.
For smokers, it is a very frequent disease but only some of them get it, not all of them. So, smoking greatly increases your risk of lung cancer. Nevertheless, if you have a particular patient in front of you who A., has lung cancer and B., is or was a smoker, you cannot prove that the smoking caused the cancer. It is awfully likely but there is always a (small) chance that the individual might have contracted cancer without smoking anyway.

That said, as far as risk factors go smoking is right up there with the big ones, secod only to (maybe) obesity. Smoking greatly increases your risk of:

• cancers of the lung, mouth, tongue, throat/lanrynx, esophagus (food pipe), trachea (wind pipe), stomach, intestinal tract, kidneys, and bladder, and probably a few more,

• heart disease (both heart attack and heart failure),

• stroke,

• COPD (Chronic Obstructive Pulmonary Disease), which few smokers have on their radar but is actually affecting millions and millions of smokers. It is what you get when a lung damaged by years of cigarette smoke goes into a downward spiral of infection and re-infection. There is no cure. Sufferers get shorter of breath little by little until, finally, their weakened hearts give out.

> So my sister was saying that AIDS is just symptom so it should be caused by more than just HIV.

I think your sister is unclear of these terms and how they are used. HIV is the virus and therefore, the cause. Its effect is a group of symptoms, collectively called AIDS.

Currently we have another virus that is all the rage: It is called SARS-CoV19, and its effect is Covid - though these terms are used somewhat interchangeably.

There is no such thing as "just" symptoms.

Also, only HIV causes AIDS. This is because AIDS means "Acquired Immune Deficiency Syndrome", with the "acquired" pointing to the fact that you get it from the "Human Immunodeficiency Virus".

There are some other types of immune deficiencies which can cause sort-of similar symptoms but they aren't called AIDS because they are not acquired from a virus.

I can‘t point you to specific papers at the moment because I am at home where my access is limited. Here‘s a link to a number of papers going in that direction. As you can see, they not only explore the location of the ACE2 protein but also the small variations between the proteins that people exhibit.

Viruses don‘t necessarily cause cells to die, or go into lysis. Bacteriophages do that, but as the name suggests, they affect bacterial cells, not Eukaryotes.

Ebola is a virus that causes cells to die and burst, which makes it so lethal.

On the whole, though, a virus has no interest in killing its host because the dead can‘t spread the virus. So most viruses that affect humans, including Covid, use different strategies. They infect some cells but not all, and the infected cells stay alive - although their function is now to produce new viral particles while their normal, healthy function is suppressed.

For the individual person, it then depends on how many cells got infected and which type they are. We know that SARS-CoV19 likes to enter the cell through the ACE surface protein. Different people have different amounts of these surface proteins on their cells, and in different tissues. E.g. if you have lots of ACE surface protein in your nose and lungs, then those tissues will be mostly affected. If they are absent there but you have some in your bone tissue, expect that area to be affected by the virus.

Then there are those who have very little ACE surface protein in the first place, so they don‘t experience many symptoms. This doesn‘t stop their immune system from attacking the intruder and making antibodies, however.

In all that is only part of the story, though. The research is still very much ongoing and there is not yet a conclusive answer for why some people die from Covid and others don‘t even notice they have it. A few predisposing factors have been identified, but Covid is not only a new virus, it is also constantly changing so that basically both the ball and the goalposts move all the time.