I'm not positive, but I don't think it was, as I'm sure I would have purchased it in HD from Amazon if it had been, and it's not in my Amazon library. After it became available in HD on iTunes, I purchased it from them for the same price as you. :)
Amazon had been streaming it in HD. Not sure why it's only available in SD now. Perhaps they had to pull the free HD version to not hamper sales of the new Blu-ray?