Duolingo needs an entry to allow "struck" to be accepted in place of "hit". The Focloir An Gúm has "hit, struck, beat" as primary meanings and struck is common in topics like this (whereas "beat" is more common for percussion instruments). Unfortunately someone configured the link to not include "My answer should be accepted" (though I have yet to confirm someone actually fixed one of these).
I don't know why you didn't see the option to report a problem, but I can assure you that the course contributors (the folks who create and maintain the course) do review reports about sentences and have added many, many new accepted answers. It really is helpful for future learners to report when an answer you are sure is correct wasn't accepted.