Thats a pretty bad mistake and should not have been put together like this. I think it shows lack of knowledge, or lack of paying attention.
At this point it should be taken completely apart, gears, hubs, syncros, bearings, should all be inspected. Then bearing end play/pre-load should be measured as it should have been.
Setting bearing endplay/pre-load is crucial as all the parts were installed into a new case, and should have been checked/set, but I doubt it was.