I'm not sure about David's reasons behind completely redacting the info, but I don't believe that was the best behavior. He should have instead left a comment and told you what to do. Even though the solution shouldn't be posted in the question, it shouldn't just be removed without saying anything.
On the other hand, this is a Q&A site, not a forum. If you have a question and a solution, they need to be posted as such, in Q&A format. You added your solution later, but it should still have been posted as an answer and not added to the question.
Luckily, in this case, removing that info isn't that big of a deal. You seem to have gotten the hint that it shouldn't be part of the question, and since we have revision histories, it's easy to paste the text into an answer. David should really have left a comment instead of just making an edit like that, but to be fair, it isn't correct to have the answer in the question. (I suspect that David may have thought you to be inactive, since it's been a couple years, but a comment is still good.)
In the future, if you have a solution to your question, add it as an answer. After two days, you can accept it, so it's at the top. This'll avoid any of these problems (and you'll get more reputation from both a question and an answer than just a question ;) ).
I see your comment under anonymous2's answer here. There's nothing wrong with self-answering. You don't get the +2 rep of accepting an answer or the +15 of getting an answer accepted from this, so the assumption is it isn't for the rep. He linked you his Q&A, so I'll link you two of my own:
Graphics issues after/while installing Ubuntu 16.04/16.10 with NVIDIA graphics
Ubuntu 14.04.5/16.04/16.10 and AMD graphics
Edits can definitely be questioned and disputed, and you did the right thing by coming to Meta to ask. Don't add it back to the question, because that'll definitely cause an edit war (it shouldn't be in the question). Just add it as an answer.