Author here. The answer is because I mentioned it as one of the bullet pointed hard-rules, and I wanted to include an example to illustrate it.

I wondered if you could sneak in some unicode digit but it seems to reject those too:

    $ go run z.go
    # command-line-arguments
    ./z.go:6:2: identifier cannot begin with digit U+0661 '١'
    ./z.go:7:27: identifier cannot begin with digit U+0661 '١'

The example with the dash in it confused me as well.

"Chat, generate me a table of bad Golang making practices"