I saw a couple examples of them sharing licensed software for free. So yes, that is my assumption. I hope for your sake that I am wrong!
If you really want to be sure, contact vBulletin directly at
www.vbulletin.com - they will tell you for sure if this supposed person works for them or not. Problem is, if it is stolen software, you will not be allowed to continue using your forum without purchasing it from vBulletin.com.
Do you have a name of this person who installed it for you? Any of the reputable people at VB would've provided a name or contact information - no shady stuff.