Sometimes I build on my friends server with custom bricks, and later on I carry on in my own server.
However I don't always have the custom bricks he has, so it doesn't load properly.
My point is that just because not all the bricks had loaded it doesn't mean he must have stolen the build.
And at any rate, it's not a crime to save/load someone elses buld. It is not nice to claim you built it, but it's not against any rules to say you did either.