I think the big takeaway for UA here is to revise their policies on how to notify passengers that they are being denied boarding due to lack of adherence to the pass-riding dress code.
This whole thing could have been avoided had UA escorted the pass riders to a private area to explain to them why they were being denied boarding. The rules for non-rev flying are very different than revenue flying. I cannot believe it has taken until now for something like this to occur.