You just have to be careful handling them if their crops are full of water. I've had them aspirate water from carrying them, but never enough to kill them, so I doubt this is what happened. When it happens here I usually notice that they start open mouth breathing, gurgling and coughing, but...
They can go from sounding fine day to sounding like they are drowning the next. When you carried him, was his crop full of water? If it was, it's possible that he could have aspirated from that, though you should have noticed when you set him down.
Very sorry for your loss. :hugs If you want to find out what he died from you should contact the diagnostic lab and arrange to have him necropsied:
https://extension.umaine.edu/veterinarylab/
It's only $25.
If you aren't close enough to drive there you can ship overnight. Refrigerate, do not...