Glad you're here. It sounds to me like you have played a lot of baseball and at high levels.
I'm assuming you're being sarcastic, but in case you're not, I just got into baseball this year
But seriously, don't you remember the "Strasburg pitches 103" and "Chapman pitches 105" and "Lincecum touches 100" and even "Detwiler pitches 94" hype? Scouts (and fans) put too much stock in the high readings on the guns.
Fangraphs is giving you an average for his fastball. It does not tell you his max. His average at 88 could mean he touches 91 when he is on.
Of course, he might well touch 91 (maybe 92, though it is doubtful), but they must have been counteracted by pitches closer to 85 for him to average out to 88... either that or he almost exclusively threw his 87-89mph two-seamer (which is possible). Either way, saying he was a 92 mph pitcher in '02 or '03 is a little disingenuous.