Vimscript String Coercion
An unique feature of Vimscript is coercion of strings into integers.
Here's an example:
:echom "six" + 6
:echom "6six" + 6
:messages
6
12
Our messages show that the first string was coerced to 0 (0 + 6 = 6), and the second string was coerced to 6 (6 + 6 = 12).
Following this logic a little further, because 0 is falsey and 1 (or greater than 1) is truthy, our first string is falsey and our second string is truthy.