In Dota 2, GPM means Gold Per Minute. The normal GPM for casual players ranged from 300 to 550 GPM (some dedicated warders/supporters might get as low as 150GPM, while carries might get 700GPM and above). While a player's GPM usually does not reflect his or her gaming skills in Dota 2, the side with overall greater GPM advantage is expected to win the match. It is rare to see a team winning a match if their overall gold earned is 10,000+ golds lower than enemies'.
Which is why you can expect Chrissy17's team to steamroll their opponents in this match. Chrissy17 used Luna in the game. And being Luna, you can anticipate a fair amount of creep stacking in the game. But still, getting 1234 GPM (yes, you read that right, one thousand two hundred thirty four gold per minute) is no easy feat. Check out their replay to watch for yourself.
P.S: Too bad there was no Bounty Hunter in the game, as Bounty Hunter's Ultimate can easily increase his team's GPM.
P.P.S: At the time of writing, the Luna player's in-game name is Chrissy17. Players have the freedom to change in-game name whenever they want, so you might not be seeing "Chrissy17" when you click on the link above, but rest assure that is the steam profile of the aforementioned Luna player.