Knowing the low level of training most security guards go through and the low level of pay they receive, you are overestimating the level of confidentiality a basic security guard would be charged with. He's just a regular old joe working for his pay; expecting actual confidentiality from a basic security guard is really expecting a bit much. Give the guy a break. Sorry, but confidentiality is not high on his duty list. It was a slip and he's just a regular working stiff.

ETA: The other thing is if he is security for the whole building and Kashi isn't the only tenant, he's not Kashi's employee; he is employed by the building owner and there are probably several different tenants of different types in the building.