In some cases, that's what happened. Lines were sometimes recorded alone in hotel rooms and sent in.
I think the claims that they recorded them in hotel rooms or whatever may have been exaggerated. I gather they just went to the nearest convenient recording studio. Still, it does come pretty close to a case of the actors literally phoning in their parts. The lack of direction did hurt their performances.
But I think this was largely a function of the insanely tight deadline the network insisted on, resulting in a very rushed production for the first 16-episode season. The final 6 episodes, which were made on a more reasonable schedule, are more polished as a result, both in performance and in animation.