Quiet Man Question, Maybe a Pub Enthusiast Can Tell Me

Okay, so I got a question about this bit in the movie:

You can to scan ahead to the bit in the pub, when O'Flynn gets the gun to fire "one if by land two if by sea" and the bartender shouts "Gentlemen on a day like this, the drinks are on the house!"

And then all of a sudden every man there paying attention drop their whiskey glasses and refuse to take another sip.

I don't get it.

I'm a teetotaler, so I'm not hep to such things.

Is that a man in Ireland pays for his drinks regardless of the free and unhindered offering of a drink?

Please comment below.

In the meantime, here's my dinner movie I'll be watching as I eat Mexican food.

...what?