It looks like the last tx out of that address was a couple of days ago to the same destination address as previously used, so I think Stedsm's funds are safe.
From searching around it looks like it is not a phishing site it's an open source paper wallet generator https://github.com/coinables/segwitaddress
But as Carlton Banks said NEVER enter a private key into a website and it would best to assume that key is now compromised.