you only gave him one shrimp to eat or did you give more after he was done eating it?
If you just gave him the one, I'd give him a couple, wait until he finishes one, then feed another. The next day, throw some mysis (small amounts) in with the ghost shrimp.
Just keep alternating 1 ghost, next day 1 ghost and mysis, next day just mysis (Small amounts) the next day ghost and mysis. Mix it up and see if he keeps eating and starts eating any of the ghost shrimp.
These guys are very hardy fish and if he's starting eat he may just be shy..
May also want to feed mysis then walk away from the tank, I found if I stood 10Feet from the tank or so, I could see him starting to eat some.
They're very shy and don't like being watched while eating... At least mine doesn't though he's getting over it pretty fast now. Even eats flake food!
I'm alternating mysis one day, flake the next. Mine is eating everything I give it!