Yep, everything seems to be on par with steam, probably the difference between numbers is because they create a specific build for GOG and another one for steam, or maybe is mistaking Hard West 2 with Hard West 1 that is version 1.5 on steam (that one I can confirm it because I own it there).

I don't know. Why don't you ask him or her?
You can befriend then PM him or her here:
https://www.gog.com/forum/pathfinder_kingmaker/instant_crash_on_load_with_workaround_stuck_on_logo_screen/post13

Maybe because people found it helpful? The readers don't know if it's true or not but they found the warning helpful.
Since it's not possible to correct reviews, that false information in this review remains there until someone reports it.
And once it gets removed, we get posts about GOG censoring bad reviews.

Both Patch 1 and Patch 2 has been released on GOG, same as on Steam. I have no idea what that reviewer means by patch 1.5 and controller support. As far as I know the game doesn't support controller at all.

There was some people requesting controller support in another forum. The dev gave some vague answers about it, and it'll probably never happen.

Yep, effectively that user is mistaking Hard West 2 with Hard West 1, check this change log from Hard West 1 on steam (https://store.steampowered.com/news/app/307670/view/2894081930487153258).
I already reported the review, that info affect the game score and make the devs lost sales.

Most probably. It's also worthwhile to mention that Hard West 1 version 1.5 is available on GOG (since 2017).