Randori is a Japanese word made of two words: RAN (or HANRAN) which means insurrection, revolt and TORI which is the noun coming from the verb TORU meaning grab. (the weirdness of Japanese language hee hee, RANDORI could even mean "translation of a book"...of course written with different Kanji).
Yes, usually when you mention randori the idea is of a person (according to the styles the person throwing can be called Tori "grabber" or Nage "thrower") having to face more opponents. As far as I know in all Aikido styles Randori is part of the Black Belt test, while a randori against opponents armed with a staff (called Jo) is part of the test for the Black Belt Nidan (2nd Dan). The ideal number of people to face is 3, more than that (I can't do it yet, but I was told by people doing it) would be too easy to have them get in one another's way.
Even tho I don't know those people I am pretty sure they are all Aikidoka, even because no teacher would risk a Uke (the person thrown) to get hurt for not knowing what he/she is doing.