It puzzles me that there does not seem to be a proper derivation and discussion of the error term in the paper. It's all treated indirectly way inference results.
Seeing the name de Vries in the first paragraph didn't help my sense of confidence either.
http://blog.zorinaq.com/bitcoin-electricity-consumption/
It's a long read to go over multiple years worth of posts and comments but gives you a measure of the man.