I think you guys are blowing this way out of proportion.
200 pushups is less than 30 a day.
He is not doing them all at one time.
My opinion would be to find out why he walked, and adjust accordingly as well.
I would probably have him run a little extra as well.
There are benefits to negative reinforcement as well.
In a society where people mostly believe in positive reinforcement at ALL times, and not hurting peoples feelings, and all that shit, he probably needs a little of this.
What would I do? I would straight up tell the kid that walking is not okay, and to try not to next time. If he can't, that's fine. He'll do more pushups or whatever until he can run. The extra conditioning will help.
It's like homework. You can't tell a kid that gets F's that it is ok, and that he should try harder. You make him sit down, and study his ass off until his grades improve, and punish him until it is accomplished by taking away TV or grounding, or whatever.
Same goes with athletics.
He's the kids coach. That gives him the right, as I see it, to punish one of his athletes accordingly, and within the parameters of that sport.
Kudos to the coach for not patting these kids on the back and saying good job, when they really aren't doing a good job.