Is the “Export to Disk” the same as Offline Compatible?"
Export to disk is the same as publish to the web, in that it produces web ready files.
Only when exporting to disk you can opt to enable the offline compatible option, which creates a different slower website that is compatible with being opened locally in the browser.
A website not exported with the offline compatible option assumes it is going to be opened from a server (so via an http:// or https:// URL), which allows for a number of optimizations that are in fact required for a fast performing site in the modern web.
Those optimizations don’t work, and break the site, when you load it from disk (so via a file:// URL).
Loading from disk is generally so fast compared to the web that many optimizations are unnecessary, so they are simply removed.
Is this the kind of information you were looking for or do you have a more specific question?
That was the answer I needed, thank you Duncan!