Hello @maxbuzz,
Actually, you are confused with the term keyword used in the plugin.
Keyword is a taxonomy, kind of category used to group the trips as like the category. How it works is, you enter a new keyword from the Admin panel > Trips > Keyword and go to individual trip and assign that trips to that keyword.
https://prnt.sc/oia7y8
https://prnt.sc/oia8jh
Finally, when you search the keyword from the filter it will display the associated trips.
As from the front page, you just search the random word which is not a keyword and you tried the same word in that filter keyword which actually shows the trips associated with the certain keyword only.
Hope this clears the confusion.
Thank you.