The process, as explained by the programmers that wrote it (which are neither me nor Chem) is as follows:
1 end of the week arrives and the servers begin the process of calculating PvP rewards and mails them out
2 the very next line of code applies decay to anyone that did not meet the activity requirement
3 characters that did not decay move up the leaderboard if possible
... some time passes ...4 player reads their PvP reward mail message which
does not state the character's rank at the time of reward calculation5 player then goes to the leaderboard and might see that they currently qualify for a reward that is higher than the one they received
so this is what the leaderboards looked like at the time of PvP reward calculation:

- pvp_results.png (33.97 KiB) Viewed 3071 times
В_ЯдD (LordXankul) was in 6th place.
Mr_Op (Salad) was tied with you but was placed in 5th because their most recent match was newer than yours.
If you scroll to the right, you can see that neither of Ceka's characters nor Barooen had any fights at all so they each lost 10% (279-295) of their points and they all fell out of the top 5 and everyone who did not decay moved up.
If you saw yourself in 2nd instead of 3rd, there must have been another match completed by yourself or one of the other two characters between the time that the data was captured and when you looked at the leaderboard.
We will be revising the weekly reward emails to show the rank you held at the time but this will require new translations and a DLC update so I cannot provide a specific date for when this improvement will be available.