Ranks displayed in PGR 3 are the position in the total leaderboard. That means, if you are rank 659 then there are 658 gamers with a higher skill (estimate) than you. This number can vary without a gamer actually having to play a game; for example, if some (legitimate) "Gotham star" gets to the top 100 players in the world whilst you are not even racing, then your rank goes down to "660" without you doing anything wrong. This "rank" can never be guaranteed to be "stable".
Roughly speaking, the change in your skill estimate depends on how "surprising" the game outcome is. If you happen to be (among) the player(s) with the highest skill in each of the games you played, then the 25 wins were not surprising and hence none of these games provided a significant increase in your skill estimate. However, if coming 5th was a rather unlikely outcome in the game were you actually did come fifth, then your skill needs to be adapted significantly. Another way of seeing the issue is that TrueSkill does take the strength of the opposition into account. One cannot simply compute the win ratio and equate this with skill; if all wins happen in the (sometimes) unavoidable unbalanced games then a win is not really testament to your (even) high(er) skill!