catered is another word for supply of drugs to celebrities, see drug dealer. If someone says the party was catered it normally means drugs are available and free.
If your asked to speak with the party caterer for a celebrity, you may well be asked to order drugs, not sausage rolls or bits of cheese on a stick!
Unless they want you to talk with the party caterer, you may want to clear that up! less embarressing than asking for a couple of bricks, and the dude in the tall white hat has no idea what you want!
"The party I went to was fully catered, I was so messed up...!"
"Charlie Sheen caterers for his guests needs!"
the line in that song the party was catered, referencing drugs and rap music!