It may be that the vet isn't used to baby birds or that he isn't used to dealing with bird handfeeders that aren't already experienced. Sometimes vets seem to expect to deal with certain levels of experience or expertise and don't know how to explain to people who aren't as experienced. I have noticed that with some doctors as well.
As far as the droopy and stretched crop. A lot will depend on how stretched it was and for how long. I have heard of many people having to use a crop "bra" for their babies until it tightened back up. The droopiness can actually cause it to be harder to digest the food again causing slow crop emptying or crop stasis. It is usually caused by feeding too much or too thick of foods or even too cold of food making the food unable to digest as normal. You could call your vet or even google a crop "bra" on how to make one and see if that helps if you don't notice it tightening up on its own in the next few days. In fact if you end up needing to use one there is a diagram on this site http://www.avianweb.com/slowcrop.html
Hope that helps