(Please be kind. I know my play in the second game was absolutely abysmal. I'm still learning, clearly. Additionally, I know that my opponent in the second game was no genius. That isn't the point. The point is that he was far more solid that almost any player I play, seeing as I generally can pick apart and shut down my opponents but he had control of me throughout the game. He didn't play flawlessly, but he played well, undoubtedly.)
Who Can Explain the Dumbfounding Difference in Skill of Players from 700-900?

People rated below 1 000 will generally make a lot of bad moves during the game, and they will hang their pieces regularly. From time to time someone will have a good game, but it can depend on the opponent as well. For instance, I can surely make a blunder and lose a piece like any low level player can do. But I rarely do it out of the blue. Most of the time, I feel uncomfortable in the position or my mind is not in the game (this is a rarer case of the 2). But if I am comfortable and my opponent starts playing badly, it is easier to find ok moves. So, your second opponent might just feel comfortable with that position and managed to not make some huge mistakes.
By the way, his play wasn't great either.
As for the first guy, he made a mistake and it was all downhill from there, that happens a lot. Psychologically it is not easy to recover from one mistake and second mistake can come pretty soon as well.
On top of all that, those are blitz games. People will play those even worse and you can't take them seriously. It will be a complete blunderfest most of the time.
Just one more thing, you are saying you are still learning. That is completely fine. If you really wish to improve, you should aim to play longer games. 15|10 should me the shortest time control, and if you can, play even longer games.
You will most likely not go far with speed chess, you just don't have time to choose the best move you can make.
Whereas this 658 from a while ago played extremely solidly (granted I played somewhat poorly):
All I ask for is a simple, comprehensive answer, because this has dumbfounded me. Some players play like they're new to chess, while others are rather apparently under-rated. I've, as black, played TWENTY MOVES OF THEORY against an opponent who was 730, in which I played the classical sicilian dragon defence and he played the theoretical counter, the yugoslav attack. He knew twenty moves of theory off the top against a sicilian, which is very atypical at my level, yet he lost the game by getting backrank checkmated...
This is a consistent theme, game after game. Some opponents play brilliant moves, some seem to have a glitchy mouse that moves their pieces sporadically.
Any justification would be appreciated. Thanks.