Most places I've been wouldn't hold this against a new grad.
However, some places might hold this against a more senior person as being tone deaf toward the position he's going to be in. Nevertheless, I might wear a suit if the CEO, CTO, etc. was going to be part of my interview loop. But, I'll probably ditch the jacket and tie for the VP of Engineering.
Well, stock advise is basically what text book publishers do.
Agreed, this is an indication of toxic culture on both sides.
HOWEVER. I would say aside from the grooming bit, the whiteboarding advice is the best possible advice for anyone. My mother can happily tell me to wear a suit, but she's not in a position to educate me about my field. A school had better fucking be, or what is the point? The technical knowledge—if they teach it at all—is itself is easier gained online than from a school.
Yikes, that's even worse. Some cultures will actively hold a suit against a candidate. I can't say I agree with that, but it's a little scary that they're giving stock advice to a highly dynamic field, very little of which is relevant. (Polite is good, being relaxed is better. Being suited is good, being comfortable is better.)