This is pretty routine in Asia - we have to send in CC auth forms with tickets we issue off an agency card the customer is not carrying when we do packages, the airline will post the authorization form to their internal PNR so the customer is not asked at check-in.

I can tell you CX is pretty firm about this for website tickets - different airlines and different airports will be more or less strict - but for a US airline? Never heard of it. Sounds like another UA agent with too much time on their hands and only a passing glance at policy and common sense.