New gamer & to POE 2

Get to endgame, start making currency, use currency to get better gear, start making better currency, use currency to get better gear, it's sorta loop pretty much. As you get stronger and endgame gets tougher the drops get better too. Plus there's now Vaal Temple that you can run which can also offer really good drops.

As a new player, you definitely shouldn't be expecting to see mirrors anytime soon - and that's fine, they're the cream-of-cream drops. 

People also quit the game after liquidating all assets. Then they just do giveaways and charity stuff on Reddit. It's a common theme, people give prize pools where the winner gets "x" item or currency or whole build. I imagine the viewer who gave 10 mirrors did the same but didn't want to do a giveaway on Reddit. But rather to their favourite streamer.

This is gonna sound stupid but 10 mirrors this league is not that crazy, with temple as it is, they drop very often

And for people who craft and play the market it isn't hard to get 10 mirrors in a week or two, if I liquidated All my stuff, I could easily squeeze ou 30-40 mirrors, but again it's just a crazy league when it comes to mirror drops and I wouldn't be anywhere close to that for a " normal" league

As a new player you shouldn't really pay attention to those players and their level of currency. They either have multiple years of play time and getting currency as a routine by now or its RMT and they don't care. Its like watching Wall Street traders and wondering how some made a million dollars in a week.