From Parole's Open Recent menu, Clear Recent Items option - this clears whole history as seen by Places plugin's Recent Document
Sean Davis referenced this bugreport in commit 4999fecc63307938d9613eb13189a368bfda9151 Clear only the history created by Parole, GtkRecentManager no longer accounts for applied filters when purging (bug #13493) https://git.xfce.org/apps/parole/commit?id=4999fecc63307938d9613eb13189a368bfda9151
Resolved with the aforementioned commit.