My friend told me he needed 25 more Series EXP to get to level 24, I found this super weird so made him take a screenshot.

And look, he really needs 25 Series EXP more to level up.
My question is, how did he achieve this?

As far as I am aware the rewards for pvp are:
CC WIN: 900 Series EXP
CC LOSS: 700 Series EXP
RW WIN: 1250 Series EXP
RW LOSS: 750 Series EXP
FL 1st: 1500 Series EXP
FL 2nd: 1250 Series EXP
FL 3rd: 1000 Series EXP

As you can see, the lowest common denominator here is 50, not 25.
The challenge log also appears to only give wolfmarks.
He also exclusively plays Frontlines.
Please help me figure out this mystery ç_ç