I think they're referring to "stupid" and "idiocy", both of which are commonly identified by ND comrades as ableist terms.

Unfortunately, they're so baked into our vernacular (same with "dumb", "moron", etc) that getting people to stop using them is difficult in the best of times. Even well-meaning comrades will use these terms without even thinking about it sometimes. But intersectionality means putting in the basic effort to change your language when it's harmful to your comrades and foster true solidarity, which is joanna's point.