I dug up the original article: https://www.politico.com/magazine/story/2018/03/09/bitcoin-mining-energy-prices-smalltown-feature-217230/

In this case, they already were exporting 80% of the hydro-energy generated, about enough to power Los Angeles in 2018 when it was written. Maybe there are some cases for your suggestion on a small scale, but if a site is generating enough excess electricity to make mining worthwhile, why would it be less worthwhile to connect it to a larger grid?