Do you think local police forces never arrest anyone mistakenly? As for civil action, anyone can sue anyone - that doesn't mean anything.
If this security guard gets a decent lawyer, my bet is that he makes money from the city of Toledo.
I've linked the actual law as evidence. What evidence do you have? Please show me where there is an exemption in federal law that allows a police officer not on official duty to enter a federal facility. If you show me this statute, I will readily admit that I've been incorrect in this discussion.
As a responsible gun owner and conceal carry permit holder, I make myself become knowledgeable about federal firearms laws, my state and local laws, and the laws of any state that I plan to travel to. I would expect that you would require law enforcement officers to do the same.