The flight attendant is not the one talking with ATC and, generally speaking, isn't even talking with the pilots as the flight deck enters a "sterile" state prior to departure.
Even when it is one of the pilots making the announcement it can vary between "we've been cleared on to the runway to depart immediately" to "we're number 3 in line and everything looks normal so go ahead and get ready" to something else. For the few United planes which have the ATC communications active you can listen to the real conversation and get a better understanding of what's going on there.