There is a blank line from find captured in the array. I think it is to remove it from the count.

That is right, I also just wanted to show you can do some basic calculation easily inline.

Looks like the last item in the all-files array is an empty string - maybe that's why? Either that, or the current directory (".") might be included as the first element.

If . was included then .. almost certainly would be as well. But an empty string at the end like you say and as explained by the sibling comment makes sense.

The empty line after the split was the reason, also to demonstrate how to do arithmetic.