95 is the last time the kdx had any major changes. Since then it's been minor & BNGs. Yes, your friend has the first of the new model (the H series), not last of the old model. 89-94 is the previous model years. (the E series)
Check out the top post of this forum (important: all kdx riders should read or something similar) & with the link enclosed you'll find a KDX timeline (along with all sorts of other information)
Yep, he's got the latest and greatest. Newer perimeter frame, new cartridge forks, improved motor and powervalve. Thats all I know about -but I probably am missing something. I think the bike was really overhauled that year after 1994.