While Janet is good and can't lie, she isn't lying by providing information about the bad place
Janet may not be able to lie but there is no compulsion on her to tell the complete truth. Besides, nobody asks her whether they are really in the bad place as nobody realises this until the last episode of series 1. When she responds with an audio recording of the Bad Place she is telling the truth: the bad place really is like that. And she isn't free to say more: she does say she can only play an audio recording and can't say any more.
Moreover, while she is a good Janet (stolen from the Good Place) she has obviously been somehow programmed by Michael to do his bidding and to sustain the illusion that his neighbourhood is the Good Place. So there may be constraints on what she can offer. She does say she can only play an audio recording and can't give more information. Presumably, if she were an unmodified Good Janet she could give more information when asked.
In short, the audio clip is consistent with Janet's nature and not, in context, deceptive.