I mean, I'm just speculating here, but that tweet makes it sound like they asked if they could add a real VPN specifically for the purposes of ad-blocking rather than for the purposes of being a VPN. And that is obviously just an attempt at an end-run around Apple's policies.

I realize the line is fuzzy here between "using a VPN to do ad-blocking" and "adding an optional ad-blocking feature to a VPN", but they are different concepts. Verizon's VPN appears to be a real VPN that simply has an optional ad-blocking feature. Perhaps the optional nature of the ad-blocking is important? I don't know.