On January 28, 2021 it was announced that [emphasis mine]
The Steward badge can now be earned multiple times for every 1,000 reviews in each queue. If you have already completed 2,000 or more reviews, we will backfill any additional Steward badges that you have already earned. You can expect to see them accrue over the next few days.
What you noticed is a result of these "next few days".
Before the change only the first 1,000 reviews in each review queue were rewarded, so one could get at most one Steward badge per queue. After the change we earn one badge per every 1,000 reviews in each queue. Past reviews were taken into account and additional badges were awarded around January 29, 2021.
It's true the user in question got multiple Steward badges in one day. The user had earned them over many years though.
AFAIK a regular user (i.e. not formally a moderator) can review 20 tasks a day per queue.