Interesting... but here's my thoughts.
The dude gave no context to this data.
Sometimes you SUBMIT your data and sometimes you DOWNLOAD the file... and sometimes you REGISTER on a website. So I don't know how this dude did the split test because lol it's obvious if you have a download and you write "Register" on the button it won't convert nearly as well as Click here or Download (and I'd guess Download would work better in this case because the person is wondering where to download the thing).
And on the other side, if you have a registration page and write "Download" on the button lol you can imagine the conversion rates.
Now of course in certain contexts certain wordings work better. And ON AVERAGE if you'd mix all these forms the "Click Here" will perform best since it's most universal, but I'd argue that in specific situations the custom wording would probably work better than "click here".
Personally I never use default Submit but change it to "Click here to submit" or something like that.
So that's that.