I came across today one of my own comments on Reddit with a search on duckduckgo. It was still intact. The problem is I used shreddit to randomise and delete the entire contents of my account. My account comments and posts all show empty on my account pages on reddit so there should be nothing.
I did a site:reddit.com search using my username and found ~50 comments that Reddit has undeleted but also hide from my own account. I could still edit and delete them. Its curious that they don't appear on my accounts content on Reddit and yet a search engine can find them and they are still served by Reddit. Ex Reddit users who deleted their account contents should be aware this is happening and report it as a GDPR breach to their respective agencies if they are in the EU if they too find this has occurred.
Search engines do not scrape the entire internet every single time someone searches. They do routine scrapes of web content and create a cache of what was there, and search that cache. This is why updates to websites do not always reflect on searches.
You're contents are findable on Google because the last time they bothered to scrape that particular Reddit post was when your comment was intact, and they have not had a need to scrape it again since then.
They are finding comments through Google and are then able to view, edit, and delete them on Reddit. They are not able to view them on their profile page.
They said the originals do not appear on their account on Reddit. They also said they edited their original posts to be empty. They're able to edit and delete their modified (empty) comments based on what I understand of their post.
I don't see anything in OP's post that indicates Reddit.com itself is displaying the originals, only the search engines are, and the cache would be the reason why.
I just did a search just like OP said and while it's true that most results are just outdated scraped content where my posts and comments have been deleted, I did find one just now that doesn't appear on my account overview, but that I could see, edit, and delete on the reddit thread itself.
The second and third sentences of the second paragraph are talking about Reddit itself. OP does not see the comments in their own Reddit page, mass edited and deleted them at some point, but is still about to find them through a search engine actively on Reddit.
They also appear when you click through the link and look at the Reddit site. They can be editted and deleted. These are not cached search results Reddit is genuinely showing those comments and yet they can not be found in your account that shows you have no comments at all. That is not what is happening here.
Do the comments still show after you empty your own browser's cache too? That seems less likely to be the culprit, but worth a check to be certain.
Elsewhere in this post there's also a helpful user who notes that the mass-editing programs can only handle a thousand comments. Is it possible this is why some of your comments are still there?
OP is not saying that Google's scrape still retains his reddit comments. He's not referring to seeing this information on Google, but on Reddit.
He's saying that reddit is retaining his comments and still serving those comments up when refreshed directly. They're de-linked from his reddit account so he doesn't see them through his reddit account, but the information is restored throughout the reddit site to be viewed.