Doesn't really matter why they didn't load in, to me. And there's really no good way to 'prove' there was a client, hardware, or connection problem. Shutting off your router wouldn't look any different than a connection drop. Alt+F4 on the client wouldn't look different from a client crash. Unplugging or even just shutting off your machine wouldn't look any different from a power loss.
LeaverBuster is already built to be lenient to one-off cases. It won't issue low priority queues to people until they're repeatedly leaving over a given period of time. If the client is crashing often enough to get LPQ from LeaverBuster, you should probably try to investigate the cause rather than just continuing to play. Do a client repair and see if that helps. If not, submit a ticket to support and they might be able to help with more advanced diagnostics to find the issue.