Well think about how ranking works.
It's designed to keep you at a 50% win rate. That means you are where you belong, with a favor to climbing since a win is almost always more LP than a loss. If you go above, you are playing better than your rank, so you're designed to climb to get to that 50% sweet spot. If you go below, you start dropping ranks until you go back to 50%.
You went up, and clearly you weren't meant for gold 5.
However, this also may not be true. If we assume Gold 5 is your playing rank, ideally you'd have gone 10/10. Instead, 4/16. Your bewilderment is coming from 6 games, as that is the differential here. Now, many attributes:
a. Bad luck. Millions on millions of players play every day, million of games. You got 6 bad ones. It happens to everyone. Most people get random terrible lose streaks.
b. Tilt. Common with lose streaks, you tilt more and more as it goes on. You play worse, blame others more, etc. If you're getting fucked in rank, put it down and do some normals. I think the gold standard that I read from some pro player was if you lose three ranked games in a row, stop doing ranked and do some normals or just take a break entirely and try again the next day. Lose streaks crush spirit and morale to the point that you'll call GG in your head when the enemy gets first blood.
c. Teammates. I know I just said up there tilt causes blame and its generally known that you shouldn't blame others for your loss. But it honestly could have been poor decisions outside of your control made by teammates. If a game is going south because 0/9/0 riven is diving 9/0/0 Darius under his tower, focus on yourself. Focus on CSing, warding, watching the minimap, ganking appropriately (Not the riven, fuck her. She's a lost cause). Focus on mechanics, predicting flashes, etc. Will you win that game? Honestly, probably not, But you'll get better. LP doesn't determine your skill, but skill can determine your rank. LP is an arbitrary mathematical formula as a reward for winning. You get LP for going 0/25/0 if their nexus explodes in the end. If you clear your mind in losing games and focus on your performance, other games you'll play better whether your Riven is 0/9 or 9/0 in upcoming games.
Ultimately, Riot isn't a massive company. It's decently sized. Millions of players, most of them low ELO. They couldn't sift through all reports and purposefully match players doing well with them if they tried. Plus, everyone has bad games. 0/9/0 Riven looks terrible. Doesn't mean she's a bad player. Could be a bad game. Maybe she's drunk, maybe her mom died, etc. It's just that game. She was in your ELO to be matched with you, so you can assume she's done roughly the same amount of winning and losing as you have.
Hope this helps :)
Edit: You also just hit gold. You're at that stage that people don't consider themselves really "Low elo" since people refer to shit mistakes as "Bronze or silver" plays. So, they think they're hot shit and suddenly all good. Toxicity is rampant. Happens in plat too because game is balanced plat+, so they think they're hot shit, and diamond because that's finally recognized as high elo. Mostly in the V's, like the guy below me said. It's the "I'm part of the big boys now" mentality,
