Odd rating climb ?

I have just played  a 10 minute game and won. When checking my opponnt's  game record I noticed that he joined yesterday as a new member and in a single game today his rating jumped from 306 to 468 ! against a 429 rated opponent ?  How is this possible ? 

The site uses the Glicko rating system that includes a measure of rating uncertainty called the rating deviation (RD) value. New players and players with few games in a pool have a higher RD value and will see larger rating changes after games.

As more games are played that value decreases as does the magnitude of the rating changes.

https://support.chess.com/en/articles/8566476-how-do-ratings-work-on-chess-com

Sorry Martin but I am finding it very hard to accept this explanation.

I've just played a Rapid game with someone whose rating has jumped up and down 20-32 points per game for all of their past six games !>????

This is the rating changes for the last 7 games

game 1 10th Feb rating 475

game 2 17th Feb rating 510 up 35 points!

game 3 17th Feb rating 478 down 32 points!

game 4 17th Feb rating 450 down 28 points points!

game 5 17th Feb rating 477 up 27 points!

game 6 17th Feb rating 500 up 23 points!

game 7 17th Feb rating 476 down 24 points!

It take a number of games for the RD value to drop a lot. I don't know the specific count but it's more than 10. I think it takes up to 20 before you start seeing closer to normal changes.

That member has an RD value of 89 for Rapid, which is still high.