• The ad was about a political stance they disagree with (Antifa)
• The upside-down red triangle was specifically used to mark groups of prisoners who participated in anti-nazi political speech
So what's the alternative? That the Trump campaign chose an upside-down red triangle in an ad at random because... it's uh... a shape?
Do they also have ads with blue circles? pink rectangles? hmm, no.
Have they also "accidentally" used gold 6-pointed stars? yes.