He's just skittish.
Our baby silver was like that when we brought him home, and he still acts like that periodically. They kind of seem to get in moods. One day they'll be crashing into the glass if you so much as move towards them, the next day they might just be swimming around happily. It takes them awhile to settle in. Ours is just now settling in and we've had him for around 2 months now I think.
He used to swim away really fast when we went to put food in the tank, now he swims at my hand when I go to drop food in.
Feed him every day, just keep it to very small portions if you're looking to switch him to something. That way he'll stay a bit hungry and be more open to trying foods. I don't believe in starving baby fish, they need plenty of nutrients and this tactic seems to work well for me with just about any fish. After a few days of this our arow has now been on hikari food sticks for 2 days, hasn't spit even one out.
Once he's eating them consistently for awhile I'll start to put some krill and stuff back in his diet for color.