That looks like a normal level of suffusion on his rump, so yes, I'd still say he's a df spangle.
It's actually much better you have two males! Now you don't have to worry about accidental breeding
Besides, two males tend to get along very well together.
Just because the other male is "approaching him" doesn't mean that he thinks he's a female, budgies of all genders who are friends exhibit behaviour that some people think is "courtship behaviour" but is really just regular behaviour for two budgies who are close friends