Yes. The FA (technically the Captain, but lets presume that this was all cleared through the Captain) can move a pax to another seat or off the aircraft. Whether it was or wasn't a good reason is a CS issue to be taken up after the flight.

Training would certainly be a perfectly valid reason as it put the FA who gave OP the boot near the presumably already-trained FA who occupied the crew seat. Other reasons could be w&b (up to the Captain if it's OK to move back).

If the only remaining seat were the single opposite the lav in the last row, that would be tough luck.