TO those of ye doing the wondering why he downvoted:
Quite simply, there's no proof on his side. While it could be a glitch, the fact remains that this issue hasn't been brought up before by anyone playing the Switch version. Ranking-down after a match on other platforms happens in the following cases:
In the second case, you'll see the result after the next game you play. As Rocket League judges your rank based on your last few results, it'll take the last 10 matches you played and get their records (W/L), and stores the current rank-up record. However, ragequitting will skip this part, and as such will mean that the current record is invalid. Rather than update it, it waits until the next game to rebalance the ranking.
As to why specifically no one believes OP, it's because his story doesn't match up. It doesn't conform with the way RL does its ranking system, it operates similarly to other platforms and acts upon the action the same way. All we have to go on for the "OP didn't ragequit" defence is his word. On the other side, we have the examples from other versions of the game and how they handle it.