Anybody understand how this chinese tablet cheated its internal storage?

I bought an android tablet via AliExpress.com, almost every review of it seems fine.

It's a "wow Monster" according to the Antutu Benchmark app.

Here's some more details, Nice? :D

BUT, the problem appeared after 3 days of using it when I tried to get my Google Drive files offline into the tablet.
It has 64GB internal storage, so it should be no problem with 13GB files of my Gdrive files.
I don't know how it was cheated but the internal storage size was NOT enough! So I removed Gdrive app and used other file manager to test it second time. I was still hopeful ...
However, check these screenshots serially!!!

Some files copied in...

Susprisingly increased size was found!!!

Here, let's continue ...

How the hell 64GB internal storage size become filled & F###ed up!

Well, very well cheated chinese tablet,