It is forgivable in the sense that he has done that a thousand times before and it's never gone wrong, but unforgivable in the sense that he knew there was a one in a thousand chance and made the decision to value celebrating and looking cool over being safe and secure.
Interesting point of law - it's definitely not out (in the same way that the Starc catch from earlier in the series wasn't out), but I've definitely seen players with less time of ball in hand and less obvious control chucking it away in celebration and that being considered acceptable. Not arguing against this decision - arguing that there are a fair few who play fast and loose and really should be a bit more careful.
Puja