If you look at the article it says:

"Our estimates factor in the total lifetime giving of American billionaires, measured in dollars given to charitable recipients—in other words, we are not including money parked in a foundation that has yet to do any good. To that end, we also do not include gifts that have been pledged but not yet paid out, or money given to donor-advised funds—opaque, tax-advantaged accounts that have neither disclosure nor distribution requirements—unless the giver shared details about the grants that were actually paid by such entities. This is a list of individuals and couples who are U.S. citizens; as a result, we excluded extended families like the Waltons, controlling shareholders of Walmart, and excluded big givers like Hansjoerg Wyss, who lives in the U.S. but is a Swiss citizen. Net worths are as of January 18, 2022."

Musk said he gave $5 billion to charity, but won't say who got it, and no one is saying they got money from Musk. So his donation is likely "given to donor-advised funds—opaque, tax-advantaged accounts that have neither disclosure nor distribution requirements". In other words, a tax write off.