Originally Posted by sudobuntu

Did you check your reservation afterwards? The agent would have had to split it. This may not be noticeable if it's your final journey leg, but if you had subsequent legs the companion would have been on a different record.

It's not a question of whether a gate agent might do it, it's a fact that technological limitations of the airline reservation system require all parties on a single PNR to be in the same cabin. Unless this agent is moonlighting as a professional computer hacker and has years of coding under his/her belt, your PNR was split.