As I wasn't there, I can't really comment on whether there is any overreaction on either party. But if those were the words used, regardless of tone (though that doesn't help), I'm leaning towards the crew not being the most professional. There are many better ways this could've been handled. On a semi-recent flight, on IB no less (which many people regard as having rude/dry/straight to the point crew, though that's not really my impression), this happened to me.

I went to the lavs at the back of J, and upon exiting, a CC said (in Spanish) "sir, I apologise but for the comfort of all passengers, you're requested to use the facilities in your cabin". I said I was in J and thanked him for enforcing the policy, he apologised quite profusely and that was the end of it. This was just after takeoff so I wouldn't have expected him to "recognise" passengers / their cabins just yet, and I'm not sure he was even assigned to J in the first place. YMMV...