My trans friend (stealth) had a coworker say "hey bud" in passing.

Like the title says. She has a co worker say "hey bud" in passing and she's freaking out. I tried to tell her that it's a common thing (this guy is older. Maybe 50s?) And that he didn't clock her. She's like 100% passing (in my opinion) and she doesn't interact with this guy often. She's so scared that she's been clocked and that hes passive-aggressively misgendering her.

She obviously can't ask the guy because then she would out herself. So I'm here asking this great community. What do you think? How would you feel being called "bud"? Is it a masculine reference (she swears it is, but google says it's not)

What advice can I give her?? Help!