Google warns site owners that they had better be using mobile-only redirects for the purpose of improving user experience and not to misguide users. In other words, some sites are redirecting mobile users to unrelated content. This may occur when a searcher clicks on a link from the SERPs and they are taken to different content if accessing the link from a mobile device. This is bad UX and is against Google’s webmaster guidelines. You can read more about sneaky redirects here