Usually flow displays correctly the topic name when new messages are added to a watched topic, but when there's an edit to the topic summary, the enhanced/grouped watchlist displays the name of the board and not the topic title.

See example where on those 3 topics in Project:Support desk the summary was created, making the entire group display the board name:

Hovering the links on each revision, one can see at least one of them has the topicsummary_revId parameter in the URL