When a new thread is created, there are two fields relating to titling: Topic Title and Topic Description. While you must enter a topic title, a topic description is optional.
In the example provided, everything after the comma was entered in the Topic Description field when the thread was created. Topic descriptions are only visible, as you say, in the coloured bar immediately above the OP when viewing the thread. In that bar, topic descriptions follow topic titles and are separated from them by a comma. In the thread listing, only what was entered in the Topic Title field is visible. The fields for the example you gave look like this:
Topic Title: Researching Allan Drinkrow
Topic Description: Allan Drinkrow
The resulting text in the coloured bar is: Researching Allan Drinkrow, Allan Drinkrow
If you enter a comma in the Topic Title field, I imagine it will show up in the thread listing but I haven't tested that so I can't say for absolutely certain that is the case. However,
this sticky thread in TNF has a comma in it and everything after the comma shows up just fine in the thread listing. I checked those fields:
Topic Title: Official TNF clothing, stickers & badges: here's how to get them!
Topic Description:
The resulting text in the coloured bar is: Official TNF clothing, stickers & badges: here's how to get them!
There is no comma after the exclamation point because one was not entered in the Topic Title field and the Topic Description field is blank.
Hope this helps