No VPN case. You busted by your ISP IP logged by HN.
VPN case. I logged in HN and gave legal advice :) Minute later I logged in Reddit, same IP, same browser, probably tracking cookies too (Reddit is behind CF too). Now CF can link my HN and Reddit logins. Chances are, I logged into Reddit without VPN days ago - IP - Busted. Not so hypothetical, imho.
In the highly hypothetical case that someone would actually investigate this they'd get this IP from HN's host or Cloudflare, then get their identity and then go forward with removing him from the bar association if found guilty.