Well, firstly, art teachers are not exactly known for their anti-feminism. Safe money is on her just being insufferable, especially given the fact that she deliberately left out what she said/did that got that response from the teacher, lol.
Secondly, this is objectively a moronic response visually. Not only is it a dial (which implicitly supports the teacher's premise), but it is plainly obvious that there is a LOT of room on that dial between the two settings--this implicitly contradicts the apparent intention to communicate those two 'settings' as a binary proposition. Would have made much more sense to display it as a switch, a device that actually has only two binary positions.
At this stage, I hope you're annoyed. I'm angry as hell, and I have no time for bottom feeders that can't look up. You should turn your annoyance into anger and fear, because the truth is, everyone should feel that way. Don't worry though; when fascism fucks up your life, I won't even bother saying "told you so."