The Balkenkreuz goes back to the Teutonic Order. The Nazis used it a lot which is why the Bundeswehr didn't, but that doesn't mean that painting a cross in a rush makes you a Nazi.

Seriously, what do you think soldiers in the field trying to not get shot at by their own guys are thinking about. I'll give you a hint: Whether it's more important to be camouflaged to the enemy or identifiable for friendlies, that's it. Ukraine is using a simplified version of the Cossack Cross for that purpose, it's a native part of their symbolism and easily distinguishable from the stuff Russians use. If everything that looks like a cross is now a Balkenkreuz and therefore Nazi you might want to take it up with various Christian Churches.

Oh and just for the record you'll get arrested in Germany for showing the Z in a Russia/Ukraine context, including as a St. George Ribbon.