I think it's plausible someone on his social media campaign saw banners with an upside-down red triangle.
I love how the goal post is moved to whether or not one existed to mind-reading WHY he might have been targeting people deliberately or why me might have used a niche Antifa logo.
edit ----
I'm sure Antifa groups attack the campaign on the same media platforms they share.
Maybe they saw it in a message or posted on a wall, who knows. The fact is you don't and I don't, why are we trying to mind-read why he might have done the worst case obscure scenario that someone suggested.
The more outlandish claim is that he was trying to demean the Jewish population with a symbol used during the holocaust.
You argue that his campaign couldn't have found this antifa logo, I argue that they weren't thinking about this holocaust symbol.