It's as well that you didn't meet me instead pd2 - You would have moved: Either the three rows back or back up the jetway to the terminal.
Weight & Balance (Trim) are not relevant once airborne - the aircraft trims itself in flight. However, for take-off especially, trim is important. Therefore. if moved, you can then move back after take-off safely.
You are entitled to an explanation, and courtesy - and then the entitlement thing stops and you are required to comply. Your 'comfort' or seat preference are factors, and ones that a good crew will manage appropriately - but they are irrelevant when given a clear instruction by a crew member, acting with the delegated responsibility of the Captain (as they are). I'm afraid this one isn't up for discussion.