As the replies title start with Re:, you can exclude them from the search result with adding -"Re:" to the post title.
For example, to get all the topics posted by Ratimov, the parameters should be set as shown in the image below.
Interesting approach, but this gave us result of exactly 525 posts, and looking at number of topics created in forum we see that Ratimov made exactly 217 topics (excluding some possibly deleted by moderators).
This means that accuracy is somewhere around 42%.
EDIT:
Correction thanks to Rizzrack, I forgot that I have some boards on ignore option so the real number of created topics is 470 currently, making accuracy percentage much higher.