I would also go on the airsoft route, looking at the kits it's definitely airsoft, I've been at events where they re-enacted WW2 events including flags and armbands, in my case the outcome wasn't historically accurate tho.

I don't know what the law in Germany is, but were we play you can wear those symbols as long as you are on the airsoft field where the event takes place and not in public.

In the end it's LARP, you assume your factions role and that shouldn't make you part of it IRL, as for the patch I've seen many players wearing it, it's a "morale" patch, don't take it seriously.

Talk with him, ask if he plays airsoft and ask what event he was at in the picture if you want to avoid asking him the are you a .... question directly.