Going into the match, Kasparov was frustrated that IBM had not shared printouts of Deep Blue’s practice games. He felt at a disadvantage because in a contest with any human, he would have a long history of match performance and would be able to tailor a strategy against that person’s tendencies and weaknesses.
My personal view is that computers should have to play candidate matches as well to get to a championship match. Well, should have, it's a moot point now that the desktop can beat the GM's.
Last I looked, computers didn't evaluate their own opening book. They are basically programmed not to play certain things. Computers should only be allowed opening books built by computers. I'm really curious if novelties would develop.
Important point is that this was not a championship match, it was just a regular exhibition match. The world champions play a lot of players in such tournaments and matches outside of the championship circuit. I doubt a computer will ever be allowed in the championship circuit .
It appears both were somewhat overly confident, so neither really pushed for this.