Other mistake: In this episode the family that John and the gang encounter are able to understand him. Yet if the planet has never experienced encounters with alien life forms, this is impossible without translator microbes.
Thank God It's Friday... Again - S1-E6
Other mistake: The planet population works in the fields, harvesting large brown biconal fruit. They seem to be heavy, as a bag containing about three of them is a burden to the person carrying it. When the leader of the planet shows one to Crighton, she picks one up with three fingers.
Other mistake: CDR Crighton is on an alien world, many light years away from Earth, but they seem to have identical—and I mean identical—Earth-type 55-gallon drums.
Chosen answer: It's never explained. John mentions a theory that his less technologically developed craft simply interferes with the wormhole less than the "superior" Vipers, but they never make a concrete determination on that point. But we also have to take into account the fact that Moya traverses wormholes with no ill effect as well.
Garlonuss ★