Can someone explain this to me?

https://m.youtube.com/watch?v=8NvTt6Vva-s&t=18215

Read this

https://crazygamenerd.web.fc2.com/FZGX_Version.html

That's interesting, thank you for the reference. However, my main question is as follows: How did he go through the door when it was fully closed?

The collision for the gate doesn' fully close until 41 seconds in the US version. The devs never bothered to update the visuals to match with the collision for whatever reason.