That definitely played a part.
I'll tell you another thing. I don't think most people appreciate how elevation can affect performance when you're not used to it.
Years ago I went to a sales conference in Denver, and the team did a hike as a leisure/team building exercise.
It was a "leisure" activity, but it ended up as a competition, a bunch of young sales bucks trying to prove who's the best.
Mind you, I'm a retired Army Ranger (was in my mid 30s at the time).
Our Colorado rep lived in Colorado Springs his entire life, was a retired Air Force mechanic. He was nowhere near my level of fitness, but he was unfazed by the thin air. I had to push really hard to keep up with him on the hike (I'd be damned if I was going to let the 75th get mocked by an Air Force mechanic, lol). I literally felt like I was going to die (of course I hid that), but I'm telling you, that thin air zaps your strength and stamina.