Were you streaming at 180mbps?

More than that, actually. I measured well over 250 over large cities. Others have reported more than 300.

That’s not how cache works.

In this case, it does. The cache for this simulator is a disk cache - and it's completely configurable. You can manually designate its size and which parts of the world it'll permanently contain. There's also a default rolling cache (also on SSD - this program doesn't even support hard drives), which does get overwritten over time.