Finder "Search" function showing every file instead of search parameter

On the Apple link that you provided, did you read the linked content named:

That is also named Narrow your search results on Mac. This describes using Spotlight-specific reserved words. Your external volume would need to be in a Spotlight compatible format and indexed by Spotlight before you can search its contents from the Finder.

If you just want to find files with names that contain a string xxxx, go to the File menu, select Find, and use the criterion that

Name contains xxxx

where xxxx is the string you want the filename to contain. If you don't specify Name contains, it will also include files that have xxxx somewhere inside the contents of the file.

This is how the search (Find, or Spotlight) function has worked for years on Macs.

The link you provided that had an example with "bike" in the search returned files that had "bike" in the filename, "bike" in the file contents, and also "bike" in the file meta data. It finds everything on the disk that has "bike" in any aspect of the file. The Find or Spotlight function has options that allow you to more narrowly limit the search.

I suggest you experiment a bit with the different search options. Try searching by contents, by filename, by date etc. using the different options. The MacOS does performs a "search" or "find" based on the options selected by the user. If the user selects no options, it will return with all files that have the text specified in the name, or in the contents, or in the metadata, etc. So lots of "finds" even if the filename does not match the search string, as one or more of those other things might provide a match.

You are welcome.