why did this player value decrease?

http://www.rubysoccer.com/game/player_info/129042

he had a initiaç value around 192000 and now, after 4 friendlies, his value decrease to 172000.

It is ok for the value to decrease sometimes, specially because the estimated value calculation formula is based on real transfers, so if the average transfer value is lower now than it was before players value tend to decrease, even youths.