It's a big, long-haired wooly roller, on a long handle, in a small room with low ceiling & the edging has already been done.
If the client is paying for the paint & roller, and the painter is charging by the metre not by the hour, he's well-motivated to be done quickly. He can get another job in, same day, new roller.
He's also not at all bothered by how much spray-off the roller is generating.
There's also a good chance it's a premium one-coat paint - again, paid for by the client.
His motivation is not economy of anything but time… & some likes on social media.
You can also be absolutely certain this is not his first rodeo - he paints for a living & has had years to get up to speed. This might also be the 5th wall he's filmed today, trying to get his time down for TikTok.
There's also method in his madness - he unloads in diagonals from the opposite end first, so there's more carry-over as he gets back to that end in full strokes.
…for sure he's picked a wall he can show off with. You're not going to gain many interweb meme points if there's anaglypta on wavy plaster, a radiator you have to work round, light switches half-way up the wall, or a 16-foot Victorian ceiling…
He's picked his challenge carefully. Big roller, small wall. It's probably a long-pile roller so it holds more. You have to bear in mind the challenge is to look good when shot on a phone - no-one except the client is ever going to be looking at the over-spray on the floor & ceiling, or all the pin-holes left in the paintwork.