Trish was already holding him for half an hour while he was being banded, measured, and having a blood test. He was anxious to go. He arrived in a carrier, of course, but had to be held for all of the above. In that case, she needed to release him directly from her arms. In that case, I think a launch must be done, for the safety of both the releaser and releasee.
I've seen raptors, including eagles, simply walk out of their carriers. As for me, the only birds I've personally released are seabirds and songbirds.