You can't say coffin corner wasn't a factor. As an example here was a Bombardier jet operating at 34,000 feet, well within it's safe operating envelope, that got hit by this because of the wake of an A380 [1].

35,000 to 37,000 feet, combined with turbulence from the weather, means this could come into play. We still don't know and may not know for some time, especially given the severity of the impact and what may or may not have survived. But you can't rule it out.

[1]: https://aviationweek.com/business-aviation/learning-test-pil...