I was talking about the 1000 vs 1024 issue, do the dd test yourself and it’s easy to verify that he was right.
As for the specific descrepancy that you’re seeing, lots of things can throw off a file size calculation - symlinks, sparse files, reflinks, compression etc. Since you’re the only one with access to your files, you’ll need to investigate and come to a conclusion yourself (and file a bug report if necessary).