Most of these residential ISPs that people hate are also major (T1/T2) upstream providers for companies like DO. If not already, at some point, these providers are going to just sniff VPN traffic straight off of their backbones.

Say your ISP is Comcast... If Comcast knows your are connected to some VPS via VPN, it's likely that anything coming out of that VPN is yours. And if Comcast (or some subsidiary or partner) is also the upstream provider for that VPS, they could pretty easily make some correlations.