Well; I'm not really sure _what_ happened... I heard them land, and then taxi to a gate, and I heard fire clear the taxiway. I'm guessing there was a medical issue?
It appears my copy/paste of the first google result was mistaken, as that tail number shows as scrapped in '98 here: Boeing 747SP Website - History for airframe# 21024 Maybe I heard the tail number wrong :/
This is pretty routine. We have these low-level standbys several times a week. Don't worry, if the s#%t is really hitting the fan, there won't be any mistaking it for anything else!