And once you make the call (with complete and total confidence), you run with that call as hard and as fast as you can. Whatever conclusion you draw as to what Manning's doing here is absolutely the only thing he could possibly be doing.
It's probably best if you assume the worst. Assume malice, while you're at it. Do all this based entirely on an internet image that doesn't show any context, any object of his gesture or really any clearly defined thing that the subject is doing.
Technically, Manning is waving his arms. Kinda looks more like he's raising his fists like a '50s cartoon boxer, though there's some sort of recoil action going on. In my day, miming a gunshot was done with fingerguns, so I really don't know what I'm looking at here. Maybe he just played Call of Duty the night before with whoever he's directing that toward. Maybe it's an inside joke with a former high school teammate. I don't know.
Maybe Manning's indeed making a shooting reference. If so, then yes, that's abominable timing and in bad taste and a sign he needs to think about things. (He does have a reputation for not thinking about things.) But I'm not going to assume all that about him right now. Thanks.