It's elementary my dear xoB,
The clenched fist can be a symbol or a salute; but, that's not how cadets are trained to salute.
It's a symbol of solidarity or support. People are asking with or for whom; because, the cadets aren't facing each other in the picture: they're facing the viewer. Who is the intended viewer they're using their military credentials to support by raising a clenched fist?
I've read the Wikipedia
List of gestures (which includes Single handed gestures - Clenched fist); also, the linked article
Raised fist and I don't see anywhere that the raised fist is a an "expression of victory" as you propose.
Of course you know a picture can be worth a thousand words, with no sign or caption needed, in which case the historical use of the gesture is what resonates. The cadets will have the opportunity to explain whether or not they were using their military credentials to express solidarity or support in a prohibited way. That's what it's about. Your contention that it's about people being offended is a red herring.
But so far these future military leaders aren't talking, go figure.
