Search in Finder window doesn't find what I can find manually!

If the external USB drive is capable of being indexed by Spotlight, then drag and drop its mounted image onto the Spotlight Privacy panel, wait five seconds, and then remove it from there. If it is a big drive, Spotlight indexing could consume considerable time. When the drive light stops continuously winking, the indexing may be done.

That external mounted drive needs to be indexed beforehand by Spotlight before that Finder Window can find anything on it, and depending on whether that external drive has a formatting that Spotlight can index.

There is a method in the madness of Spotlight searching further aided by reading the Finder's Narrow your search results on Mac, and the individual search result categories that you have selected in Spotlight Preferences.

With proper indexing, and the drive mounted, I would search (case-insensitive) for your highlighted .wav file as:

kind:audio +.wav name:"13 all will be well vmc2"

I have narrowed the search to a specific kind of audio file, and the name operator to focus on file or folder name strings. Just typing in the unquoted, text string tells Spotlight to search for each chunk of text which will be frustrating. Once can also use just name:.wav to see all these type of audio files.