This doesn't really excuse what happened but hopefully things are a bit clearer. The first draft of the script did pretty much the same thing here but there was a bit more of an actual fight between the two. Evey actually hits Izzy with the Mallet in that version which causes Izzy to strike back and basically fly into a rage. This all happened at street level too so there wasn't any falling off of buildings or anything.
As you can probably tell, this is not something that would've fit the story or these characters. But it's still far closer to something that could work than the original outline which would've seen Izzy go full-on villain. Izzy's not really a villain though and Evey would never fight their friend unless they absolutely had to. These things just aren't in their nature. So I decided to make this more of a tantrum than a fight. That was a sort of painful change because I really wanted that fight.
This isn't the end of the chapter by a long shot, but I hope you've been enjoying it so far.