Here’s the actual criminal complaint, with the mall cop’s report, courtesy of The Smoking Gun.
Looks like the lawyer and his son were first challenged because they were making a disturbance, not necessarily because of the T-shirts. The mall cop first asked them to “stop bothering other patrons” and “cover or remove” the T-shirts. The lawyer desisted from bothering the other patrons, but refused to cover or remove his shirt. Only then was he arrested for trespass.
Looking at the report, I think it was, for the most part, the T-shirt that got him into trouble. The initial complaint was about the disturbance, and the lawyer ceased that. The T-shirt issue only came up later (don’t know if the other patrons in the disturbance had demanded that he cover or remove it). True, he was arrested for trespass, but trespass wouldn’t have been an issue if he hadn’t been asked to remove the shirt in the first place.