I don’t think he meant it in a negative manner but you have to understand that it most certainly came off as rude and inappropriate, there is absolutely no reason you should not apologize. Heck I wouldn’t even necessarily apologize to the friend but the actual mom, no matter what the context is you don’t go around calling someone a hoe, especially if you don’t know the person. Also even it being a joke is still somewhat disingenuous like if I say, “oh your mom is a hoe” in front of both of them and then say some bs like, “it’s a joke” it still doesn’t make up for anything, apologize simple as that. Again it even seems like his friend didn’t react very well to the situation, another reason to apologize as they clearly didn’t like the joke. Like if my friend called my mom a hoe in front me and my mom I would feel uncomfortable as well.