I admit I'm not a huge fan of the "What aboutism" and it doesn't look any better on liberals than it does conservatives.
So to address the OP regardless of how futile it might be, Biden is old and at a certain point old people just kinda stop giving a shit.
Biden just wanted to get a rise out of a little kid and didn't do some generic manufactured baby smooching thing that didn't play well on camera.
"You're so sweet I could just eat you up" is such a common turn of phrase for oldies to say to kids and babies, I can see what he was going for here.
Unfortunately shit like this will be used in the conspiracy theory circles as more "proof" and that the mask slipped somehow (and was exposed on Yahoo news of all god damn things).
I'm not a fan of it either, but what's going on here isn't really whataboutism.
Whataboutism is when figure A and figure B have been doing comparable things and supporters of either group are more critical when the opponent does it but more passive about it when their guy does it. Biden's and Trump's actions are not even remotely comparable.
Whether this incident was Biden doing it, Bernie, Trump, Boris Johnson, Jacob Rees-Mogg or Adolf freaking Hitler, it's not even remotely remarkable IMO. Even FDC and Greenman despite stating that it's "creepy" can't even express a solid argument about why anyone should give two shits about it. IMO the only remarkable thing about it is how the right-wing media has conservatives (like these two plus blackangst1 on the P&N humour thread) so well-programmed that they respond identically and none of them demonstrate any kind of basis for their reasoning; FDC started blathering about illegals, blackangst1 going to far as to say he'd knock a elderly stranger out in a supermarket if they did that to his daughter and he thinks that everyone else here would react the same. It's fucking 1984-daily-hate weird.
Coming back to this 'current event' - when I was a kid, one of my uncles had this routine each time they saw me / my siblings where they would do this pantomime that I think was something like mimicking putting an imaginary person in a headlock (or something similar) and saying, "get out of that". It was an odd thing to do and I don't recall that we ever played into it at all, but that topic in our family barely warranted two sentences said about it in total, ever. To my knowledge that uncle didn't do ever anything else that was remotely suspect. This story seems about as remarkable as this anecdote with my uncle, a person that I have no great attachment to.
I'm almost curious enough to search this forum to find the original discussion about the outrage surrounding Obama's tan suit; I bet his detractors here were showing a bizarrely stunted ability to express their problem with it then as they are with this topic.