The guard *might* be to blame. I work as a guard, and I'll tell you that a lot of companies don't actually care about security. They pay their guards next to nothing, so they can claim they have a guard and get a big discount on their insurance (much bigger than the expense of the guard).
Not true everywhere obviously, but a possibility to consider.
No. Obviously someone from the commercial sales division let the customer in and then sent him on to Dilbert. Stupid and incompetent. The security guard is not to blame!