[HMM I OFF TOURNAMENT] "Company"

...or, if you're playing as a Wizard, will you not encounter other Wizards at this stage of the campaign???

That's absolutely correct. There are only 9 maps in the campaign, but since 4 of them are played specifically against one of the factions, one map will constantly be "skipped" because in Heroes of Might and Magic I, it's impossible to play with the same faction for two opponents, whether it's player vs. player or player vs. computer. Since this campaign is for the Lord Ironfist (Knight) faction, map #5 (against Ironfist) was automatically skipped, and the 5th stage was on map #6.
P.S. It seems you were playing as Lord Alamar, and map #8 was skipped.