If you were a building owner, would you allow your tenants to modify the fire sprinklers? If not, how did they get entry into the building's mechanical areas? Building Security would have had to let them in and they would have called for authorization. Sorry, all of that sounds VERY fishy.
Bingo. The sprinkler system is an integrated system;therefore, it is unlikely a single tenant could bring in un-licensed plumbers from a company in business for less than 18 months that was not listed in the phone book to work on a system critical to the safety of the entire tower.