This one seems to be present in the database, but the title is in all-caps for some reason. So, not the same problem.
In your case, have you imported the games you didn’t install from website (like your Steam library)? If you did they might interfere with stuff you may be trying to import. I don’t think Proton plays a role in it (rather it may be the difference between game title in Steam DB and in Lutris DB) as I’ve imported quite a few titles installed via Proton without a problem, and most of them (if not all) have no native Steam install scripts (Proton or not).
You could probably pull it off same way as I did with LEGO LotR – remove it from your Lutris library, import the Proton version and replace generated identifier with the one on website (after restarting Lutris it successfully synced the icon from website).