We all know the issue here. It's a silly out-dated rule, but it's too expensive / difficult to change it, so the rule remains. But everyone knows it's silly.

So, the FA does follows his / her training and makes everyone power down, following the letter of the rule, but then ignores the letter of the rule and follows only its intent. A well-run airline would have anticipated this problem and trained for it in advance. An adequately run airline would issue an informal reprimand and beef up its training. A badly run airline would ignore it.

I hope UAInsider follows up with the OP and tries to obtain details so that UA can pursue the matter further.