I've got a '02 TL (225 hp), it's pretty quick, probably in the mid 15 range. I've got plenty of friends w/ TLS' and CLS' and they run anywhere from 13.9-15.2. I know of one person who got 13.5 w/ an 80 shot NOS setp (didn't see that one though).
I don't think it's impossible that this guy was able to beat a Mustang, but it sounds odd that he was lucky enough to roll up on 3 Mustangs that were all that slow and/or drivers that couldn't drive.