did he say how many poeple roughly are on the "high alternate list"?
No, he didn't mention that. If I'm not mistaken, they interview roughly 500 students for 100 seats plus 40 spots for the waitlist. I don't know if they evenly divide the 40 into high/mid/low tier waitlist though. I don't think that part of the process was ever explained, maybe because no one asked that day.
I've been living on my nerves since the interview though, so hopefully someone else here can confirm.