Repeated keyboard speedruns can only be done with certain keyboards that are able to handle multiple inputs at once if you hold down multiple keys. The runs are absolutely legitimate and were made their own category for a reason.
No. You are able to hold down multiple keys at once and the keyboard will read all inputs. You can "spam" arrow keys and the WASD keys in both NKRO and non-NKRO runs, but to achieve at least the 2048 tile, you need some semblance of skill and ability to merge your tiles together; you can't just "spam" your way to the 2048 tile.
"It's not even a speedrun, it's just a joke." Is wild coming from someone who has never seriously tried it. While the times can be pushed further back than without these repeats, it still requires a ridiculous amount of grinding. Yes, getting a sub 40s 2048 is significantly easier with NKRO, but getting a sub 20s 2048 would still require just as much skill as a sub 30 non-NKRO. While theoretically it is possible to use these repeats to get a 2048, it is statistically extremely unlikely, and it has also never occurred in the past. thecabillonaire is right, you can't just spam your way to it.