As all stated above, he should be fine unless you already got a sick fish, sorry to say this but it happens sometimes.
However, as you already told that he ate some bw, his diet should be fine.
Mostly it's just stress, so keep feeding a little until he is 100% feel secured in the tank.
Some questions, had your tank been fully cycled, new media or fluctuations in temperature.? Perform water changes and add some stress coats, Aquarium salt wouldn't harm in little quantity.
Any decorations might sometime scare the new fish in tank.
Your observations for couple of days is the key to recover him fully.