The way I bought it was by going to https://www.factorio.com/buy , putting in my email, and pressing "Pay with Card." That redirected me to Humble Bundle where I input my credit card information and bought it. It sent me a receipt, and then (because I accidentally checked the "Send as Gift ...

Purchasing on humblebundle.com requires an humblebunlde account, so if you don't have such an account, how did you buy the game?

Not sure, I put my email in and requested a password reset to check and see if I do have one, but the reset password email says:
"You are receiving this email because ...

Well, I'm trying to buy this game because the demo got me hooked, and everything went fine until I went to get my website key. I payed via credit card on Humble Bundle, got a Factorio account, verified my email, logged in and pressed "Upgrade," but when I pressed "Reveal your Factorio key" on the ...