It depends on the job fair. My university’s job fair was as you describe. From talking to (women) classmates who attended Grace Hopper it sounded very worth it. The lines were short (in the mid 2010s anyway) and many of the companies in attendance were scheduling next-day, single round interviews with offers sent out by the end of the week. I have no idea if it’s still like that but I can’t say I’m surprised that male students have gotten desperate enough with the current job market to see if the stories are true.