Many factors could have come into play.
- Mental state: Believe it or not, from day to day, or even from game to game your mental state can vary significantly enough to cost you games/ win you games. Depending on mood and mental fatigue an individual can go from playing at a platinum level to a silver level.
- After the loss streak, your MMR fell and you fought worse players, which made it easier for you to win games and propelled you forward.
- bad RNG combined with bad gameplay: basically what's happened to me in the past goes something like this, I fucked up two games in a row, and lost my games, even though my team was not bad. Then the next two games I played flawlessly, but someone on my team fucked up and lost us the game. What should have been 2w/2L turned into 4L.
These are some of the things I've found to effect my streaks, could be something entirely different for you.
If people tell you riot matchmaking is controlled by sentient lizard people that secretly target players to force them into a 50% winrate, dont listen to them. It's pretty simple, If you're better than your current ELO you will climb, if you're not you will stay in the ELO you belong. Players who are amazing/smurfs can climb quickly, players who are only slightly better than their elo will climb more slowly, but they will.