Perhaps they share the same entrance, but if not, it may also be the case they made a stupid mistake, thinking they were being sarcastic with the flag, and it backfired on them, so now they are claiming innocence.
I wouldn’t assume they’d lie. It’s not unheard-of, of course, but apparently the photo shows it’s at the other tenant’s entrance, but some activist sent out an alert, which went viral, which specified the other address (entrance).