A question about first boss

[Lasiurus]

OK, so far I'm liking this game, however I have a doubt:

First chapter, I reach the end boss, the wizard.

So he started teleporting himself and my bullets wouldn't hurt him, so I started focusing on the minions he summoned, I noticed that when killing his minions his lifebar woul go down slowly. Eventually, once the wizard's lifebar became very short, a cutscene starts, in it, the wizard jumps down and levels with me, he summons this kind of pink shield and the main character comments on how the only way to kill the wizar now is by using melee attacks. But then, right after the cutscene ends, the main character says something like "ha, you didn't liek that very much", and the boss is defeated, a door open and a soldier hits me with his rifle, the level ends, and I'm prompted to advance to the next level. The problem is... I never foughr the wizard, its like I skipped the second part of the fight... Is this a bug...or is it the way its supposed to be???

THX..