ratings
The site uses the Glicko rating system which includes a Ratings Deviation value (RD) that is a measure of uncertainty. New members and members with very few games, have a high RD value and wins/losses can cause large swings in rating.
The site also allows new accounts to set a skill level, so it is very possible that they choose an inaccurate skill level and playing a few games will quickly put them closer to their true strength.
Glicko RD also has a time component. If a player doesn't have many recent games, the RD value will increase, again causing larger rating swings.
https://support.chess.com/customer/en/portal/articles/1444777-how-do-ratings-work-
If you need help, please contact our Help and Support team.
I've played several times against players with ratings that decent and then after the game their rating shifts considerably lower. How and why would somebody camoflauge their rating?