Hello,
The KoBo behaviour seems to be contains (not equals). You may have a look at a previous posting, incl. a github link
https://community.kobotoolbox.org/t/filter-appears-to-be-a-sub-string-match-rather-then-the-exact-match/12347.
But maybe @Kal_Lam can say how a complex condition can be entered in the KoBo filter cell. With an ¬ condition you might be able to limit the search further.