It was unnecessary, especially as the OP was being courteous letting them pass. I often allow crew to pass, given how busy they are, and would expect a thank you, just as I would if I let other passengers past. The crew should check their facts before rebuking passengers, if indeed their job description includes rebuking passengers. And when they discover they're wrong (which they clearly will have done in this case ) they should apologise. It's common courtesy, in any walk of life.

If the tone of voice was unpleasant, and given that you were using a bathroom you were entitled to use, I think this is cause for complaint. How will crew learn that this is not the way to behave if you say nothing?