In regards to his stats; unlikely. It took a Chaos Empowered Horus to really threaten him, but it was still Horus who saved his life when he was being throttled by the Gigantic Orc. That stormbird ruleset is ~4th edition Apocalypse rules, but fan made.
Well actually the one you are talking about is Gharkull Blackfang and thats not him he was on the planet of Gyros-Thravian.
The ork that choked the Emperor was "on the Ork-infested planet of Gorro, Horus repaid the debt by hacking the arm from a huge, frenzied Greenskin warlord as it struggled to choke the Emperor's life out of him." From Luna Wolves Index Astartes. For all we know it could have been a test for Horus, Emperor was busy killing other stuff, sneak attack, or combination of anything else.