T's and C's on FIFA's site are pretty clear:

  (i)            FIFA Content

  5.1          All FIFA Content, including FIFA feeds, is owned by, or 
     licensed to, FIFA. FIFA Content is provided to You “AS IS” and may
     not be used, reproduced, distributed, transmitted, broadcast, 
     displayed, sold, licensed or otherwise exploited for any other 
     purposes than their access and usage on the FIFA Digital Platforms.
     For that sole and exclusive purpose, FIFA grants to You a limited,
     revocable, non-exclusive license to access and use the FIFA Digital
     Platforms privately for non-commercial purposes, in accordance with
     these Terms.

"FIFA Digital Platforms" is defined as the website and their App.

So... doesn't really sound like an "official API" in the sense of being something you could use to create your own world-cup data-based apps or web sites...

Is there any documentation for that api, from the url it looks that they created it specifically for their official mobile app only?