Sorry, but what exactly is a “sustained download event” supposed to be?

I’m pretty sure they’re describing something akin to what many small site owners have referred to as ‘the hug of death’. If you’re a small site that blows up on the front page of lemmy (or an actually large community site), you’re going to experience sustained traffic that your site isn’t capable of handling (be that at the computer resource or financial level in this case).

Normally the hug of death’ just takes you offline when your provider can’t handle the load or you blow past your providers thresholds. In this case, that threshold didn’t appear to exist and it just kept adding to the bill.