just as i said,I dont know why it can run it when all data didnt finish, 38% data include what can run test mode model or material or someting else?? Total 20.5GB game memory，38% of 20.5GB is 7.79GB，The Game likes Apex legends  which is so excellent,just need 7.79GB to start the game, i think this is amazing,what do you think? 

Well, if you ever used Blizzard Battle.net.

Most of the game are like (i.e: Wow... )

An easy explanation is to download at first low quality assets and/or even make the game skip some elements since you will not be able to see them till midstage or whatever of the game.

I remember in who I was trying to go through a portal, but didn't teleport because I didn't download the part behind it

For example, in Mortal Kombat X you can start the tutorial before the download is finished. Because, in the tutorial, there is only one arena, and there are only Scorpion and Sub-Zero. So the game downloads the main game, one arena and two characters, and you can start the tutorial. While you play the tutorial, the game can download other characters, arenas and all extra content.

It is probably the same with Apex Legends: you don't need everything to start the game, so the game downloads the things you need first. Then, when you start playing, it downloads everything else before you need it.