I had to check if this was true. So, Jupiter is about 10x the diameter of Earth, which means it has 100x the surface area. So while it would still be possible to travel anywhere by jet, it would be impossible to travel everywhere in one human lifetime (e.g. there would be 100x the number of cities, nations, etc, and it's already unlikely that any human has visited every major city). So yeah, tentatively I think it's true.