I do think that there is some truth to the idea that sometimes the devil you know is better than the devil you don't. There's also all kinds of "grass is greener" situations in which you jump ship and don't realize how good you actually had it.

I think he's just saying if you love your job, don't throw it all away due to a supervisor's comments giving an undertone of something. It's worth having a conversation with that supervisor first. Their response to your conversation may result in things getting better. Or it may result in a confirmation that it is indeed time to look for a new job.