I bet no male teacher was ever called out for looking inappropriate at work.
As a former male public school teacher, I can assure you that the assumed premise behind this statement is utterly FALSE. If a male teacher showed up for work in shorts, or flip-flops, or a wife-beater undershirt at any of the schools I worked, they would most certainly get called out.
The main reason for what appears to be sexism re: professional attire is precisely because the standards are stricter for men. As a man you pretty much know what’s expected of you for work attire in a professional environment: slacks, dress shirt (short or long sleeve depending on weather), dark shoes and belt. You may get casual and go to jeans and polo shirts on occasion but anything else rightfully opens you to criticism.
What that woman is wearing is more appropriate for a night at a bar. The choice of footwear is also foolish for a classroom — just asking for a broken toe or foot if a kid brings a chair leg down on it.