I wonder if someone rented the rink for a “party” then SOLD tickets (skating, food, byob) to all comers. Rink refunded the original renter. But did the renter stiff the ticket buyers, and say it was all due to racism to misdirect the crowd’s anger?
Perhaps the rink has the “off-duty deputy for security” requirement to discourage this sort of thing. Police presence is the last thing these sorts of partiers want. And what lone off-duty cop would agree to try to keep order in a crowd of 400 thugs?
I think your theory may be likely.