That was a really badly worded Tweet.
The ERCOT grid lost 3,000MW. Riot's (brand new) facility has the capacity of 700MW. They are not yet at capacity, I believe, but their website apparently shows their capacity utilization plan:
They did not say if the are curtailing for only their own self-mining (probably ~200 MW now), or if they are curtailing for hosted (customer-owned) equipment as well (probably close to another ~200 MW). Presumably the customers would have the option as this is a voluntary act in response to ERCOT's request, and not contractually required nor an order by the gov't.