No, you aren't obligated to cancel, but if you are still within the 48hour full refund period, you could, as hosts get severe penalties for cancelling a reservation.
It could be that the host forgot to update their pricing, and in that case, the onus is very much on the host to cancel. But honestly, "glitch" is not necessarily an excuse- the Airbnb site has tons of glitches and hosts post here all the time wondering why their pricing suddenly changed, or their check-in time changed when they didn't do anything on their end, etc. It happens all the time.
And if it truly is a glitch, the host should contact Airbnb to find out why the price showed incorrectly and get Airbnb to do a penalty-free cancellation. But their customer service dept. has been so poor lately that hosts are finding it frustrating to try to get the simplest things taken care of.
@Cynthia824