Try doing range based keywords in Premiere Pro. It is impossible. When doing keywords in FCP X we need to have a naming convention that makes sense so you don’t have them all over the place that does not make sense. Using a phrase from an interview and then not putting that into a folder with the name of the person who said the phrase might not work as well instead of creating a folder for each person that was interviewed and putting it in there. You could use a folder or an event for that purpose. I am not saying this is the best way but there are many ways to go about it. I have tried to do this in PP and it’s not happening.
Kind of weird behavior in FCP X. Keywords from the finder seem to be searchable but keywords created in FCP X are not if you just type the word in the search field. But, if you have more than one word as your keyword the first word will get results but if you have two words or more and type all of them it will not get results.
Keep in mind If you have an event selected your search will only search in that event. If you search a library it will search in that library. I am not sure about keywords as finder tags. I will need to try that.
Unfortunately, you can only search keywords this way, or toggle the event down to see the keywords for that event. If I had that many keywords I would create folders to help organize your keywords. Do You have a link to the tutorial you saw?