a) demonstrating a lack of burst or headroom capacity and/or graceful degradation/priority scheduling capability, and
b) being a dick about it.
Alternatively one may intervene with a positive approach and framing viz. "we have temporarily [provisioned additional capacity / relocated your storage to another spindle / mirrored your content to a less congested host / etc] in order to handle your traffic, can we call you tomorrow to move you to a service plan that can handle your growth". Even just throttling the account in some appropriate fashion would've been better than the blunt "we dropped you like a hot potato" that was actually communicated. This was in 2010, by which time any ISP that wasn't operating as amateur hour had the tools for all these things.