They peaked at 57k simultaneous viewers, which would be a very popular stream on Twitch. It's about how many viewers used to watch Trump press conferences, SpaceX launch streams on YouTube, or developer streams for AAA game developers. The top daily streamers on Twitch get about 80k-100k, and specific events like tournaments can go up to 400-600k.
The fact that Sam got that many viewers on his own website, without platforms or algorithms or random recommendations, is very impressive.
The bandwidth problem is that each of those viewers wasn't watching 1 stream, they were watching 10 camera feeds at once on the Fishtank page.