So about a week ago moon and I had agreed to play some rapid games and analyze them together on a discord vc, which we did publicly. The score ended up being 1-1, with moon winning the second one and me winning the first. Both were pretty wild games, but since I only have a limited amount of time on the internet and I want to go and play some video games now, I have limited myself to only annotating the one I won ( in order to increase ego size ).
On the explanation of why white's 5.g4? is a serious opening mistake...
Basically, when you're in a lead in development, you wish to open lines. Black, conversely, wishes to keep them closed until he can group his forces sufficiently. g4 looks aggressive on the outside, kicking black's h5 knight and gaining space, but in fact this is all an illusion. White, having wasted an entire move to force black's knight to go somewhere it was going to go anyways, has, simply, overextended. Black strikes back with ...h5, and either forces the position to be completely closed, or forces white to split his pawns and recieve h file pressure after gxh5 Nxh5.
Long story short, white forces black to play good moves and cannot consolidate himself in time.
Therefore the advantage goes to black.