TikTok search isn't a search feature. It's a content discovery feature. They're extremely transparent about this and have a whole programme for telling creators how to use it. That's why it caps out after a very small number of videos relative to how many are on the platform. When you search for something, TikTok shows you a very limited selection of videos that mix popular and new content.
It doesn't want to help you find something specific. It wants to help you find videos or creators you'll engage with and offers you a mix of new/successful content to choose from to help drive account discovery. The videos being mismatched is a mix of TikTok's search being simply bad and an attempt to push diverse content on you regardless of what you're looking for, and sometimes from creators gaming their descriptions and hashtags and video script to reach different search terms.