Where they there to see it trapped? Then how do they know!?
I see you're keeping slashdot's tradition of not reading TFA. Here's what the very short article says about that:
To date the water, the team used three lines of evidence, all based on the relative abundances of various isotopes of noble gases present in the water. The authors determined that the fluid could not have contacted Earth's atmosphere — and so been at the planet's surface — for at least 1 billion years, and possibly for as long as 2.64 billion years, not long after the rocks it flows through formed.
This year I turn 6.
A year is a period of time, not the occurrence of a specific date.
Top Ten Things Overheard At The ANSI C Draft Committee Meetings: (5) All right, who's the wiseguy who stuck this trigraph stuff in here?