This forum is really funny… As I went thorugh it, lot of users asked a question and after several days they answered for their own question, because nobody replied….
I have also seen this before, especially on topics more than 2 years old, but less than 5-6 years old. There was some users that have had moved on from helping out in the support forum. If it happens now usually it is when, I or someone else may not know how to help on some questions (happens on something I am not familiar with like app development or other custom development), we are busy, we could be sleeping and someone figured it out overnight. .
As for this topic, I may have over-thought it a little.
If you do want this kind of layout across your entire forums on your site, I do not have the time to do that right now. Here is what you wanted in this single-topic.php file that should be placed in your child themes root.
https://gist.github.com/robkk/d0682447a3cbdf9807a1
Here is what it looks like. IF you need to modify something in content-single-topic.php just edit this template since I just copied it over.
