You will also get different results by gpu, compiler, kernel, architecture, and then of course compositor. Even a slightly different version of some lib might throw off the results.

In any case the methodology in the post is sound and should be used for benchmarking in the future.

And FWIW, KDE probably make the most effort with their compositor. They have historically been well ahead of the curve for things that might affect this (e.g. VRR).