If I would take a guess about a total stranger, it appears that they are a printf debugger. No shade, I am too. But it's not a huge leap to go "the thing I do with errors is print them to the screen, and you print strings to the screen, so strings make sense as error conditions."
Furthermore, they seem to enjoy Go, and Go's version of Rust's Error trait provides one method, Error, which returns a string. While I haven't written meaningful Go, and can't speak to its idioms (though as far as I understand, "just turn it into a string" is not idiomatic Go), it's another sign pointing towards "the easiest way to handle errors is to just turn 'em into strings", especially if you're just trying to ship something and don't care about the details.