Yes, an extremely poor user experience is a ranking factor, according to the official statement from Google quoted below.

“we developed an algorithmic solution which detects the merchant from the Times article along with hundreds of other merchants that, in our opinion, provide an extremely poor user experience. The algorithm we incorporated into our search rankings represents an initial solution to this issue, and Google users are now getting a better experience as a result.[…] We can say with reasonable confidence that being bad to customers is bad for business on Google. And we will continue to work hard towards a better search.” source

I believe that when Google mentioned “user experience” they actually meant “customer experience”. User experience relates mostly to the experience on the website (i.e. simple navigation, safety, usability, etc), while customer experience goes beyond websites; it’s about the post-purchase or post-service experience (i.e. shipping, installation, etc).

Of course, Google penalizes poor user experience (i.e. Ad-heavy penalty), but with the update mentioned at the top of the article, they have included signals that go beyond the website. If you think about it, Google requests their human quality raters to evaluate third-party business reviews to gauge how much to trust a business.