Yeah, they're either talking about the site that you're ultimately connecting to, eg the bank, social media etc, in which case doing it over a VPN doesn't magically help you if the site is dodgy, or I guess they could be talking about the portal site for accessing the public wifi in the first place, but again a VPN still wouldn't help with that since you'd need to connect to the wifi before starting the VPN.
Would have loved to see the ASA respond simply by saying "That's nice, but what the hell has that to do with what we're discussing here right now?!?" :)