I'd like to see evidence of this "rides" thing too. It looks to me like the DM is calling for a check simply because the player described a task that sounded like it aligned with a skill proficiency without taking into account whether there is a meaningful consequence for failure. In this case, the PC is sneaking around. But if there's nobody there right now to notice them, then there's no reason to make a roll because there is no meaningful consequence for failure. Instead, the DM calls for an ability check when it's relevant to do so, such as when they approach those aforementioned guards. This "rides" ruling looks like a fix for a problem that is occurring at the point of calling for a roll without a consequence in the moment.