Baggy T-shirts, layers and hoodies do a good job of hiding the girls. Unless they're paying attention it's not hard to miss.

Yeah. Weirdly chest fat is not a huge gender indicator for a lot of people unless it's called attention to. I've known several trans guys with big chests who pass just fine.

The biggest indicators imo are hair: haircut, facial hair, and body hair; then voice, then height, and maybe chest/hips/muscles somewhere after that. With a hoodie most people don't even notice.