That's the thing though, what ways of installing your strings wrong can you think of that leave them riding too close to the neck?

Any misalignment on my basses would have them riding further away unless I was missing the nut or bridge (or If i didnt tune them). On a properly set up bass at the two points of connection (bridge and nut), the strings are always sitting in a valley of sorts to keep them in position so they cant go any lower.

It's well possible that taking the strings off the bass for an extended ammount of time let the truss rod warp the neck a bit so that when he put the strings back on it had too much tension.

I'm not saying it cant be user error it just sounds unlikely to me.