Maybe the disk size 7TB and there was nominal size data on it after the OS and updates were added and the vast majority of the 7TB was empty disk space. It is possible.
Have you ever thought that these 7TB could refer to contents of other projects that the owner of ChipMixer had?
But even if it does, do you think that in 10 years of running the mixer, it would generate 7TB of transaction logs? I honestly have serious doubts, just look at the size of the Bitcoin blockchain, which is around 500GB. Of course, that doesn't mean that in the middle of those 7TB there are some logs.