Wouldn't Arnold credit himself? Weird for a bodybuilder to miss a chance to big himself up.
I've always wondered that myself.
The previous photo I posted, was obviously taken prior to his return in 1980, so that means it had to have been taken in 75 or earlier. My guess, though the guys at IronAge (or ND) could tell more about it, is that the photo is around 73 or 74. That means the photo is at least 8 years before Samir showed up in his phenomenal shape on 83.
I'll take a gander and say that when Arnold appeared as he did above, they just didn't have a name for the Christmas tree lower back and when Samir displayed it, someone said "My God, his back looks like a Douglas Fir Christmas Tree!" and thus the name was born....