There's a "Topic" option in the namespace dropdown menu at Special:Contributions - however, an editor's contributions to Flow discussions, are not listed there, but only in the actual namespace indicated. I.e.
https://en.wikipedia.org/w/index.php?limit=100&tagfilter=&title=Special%3AContributions&contribs=user&target=Quiddity+II&namespace=2600&tagfilter=&year=2014&month=-1
vs
https://en.wikipedia.org/w/index.php?limit=50&tagfilter=&title=Special%3AContributions&contribs=user&target=Quiddity+II&namespace=5&tagfilter=&year=2014&month=-1

Expected (?) : if this namespace is not intended to be used as a "contributions" tracker, then possibly it should be removed from the dropdown menu, to avoid confusion.

If it is intended to be used as a tracker, then possibly a user's contributions to Flow Topics should be listed in both sections? (e.g. both "Topic:" and "Wikipedia talk:")

The confusion is partially due to:
In RecentChanges, the contributions from editors *do* appear in the Topic: namespace. I.e.
https://en.wikipedia.org/w/index.php?namespace=2600&tagfilter=&title=Special%3ARecentChanges
vs
https://en.wikipedia.org/w/index.php?namespace=5&tagfilter=&title=Special%3ARecentChanges

More discussion at https://en.wikipedia.org/wiki/Wikipedia_talk:Flow/Archive_11#Contributions_to_Topic_namespace