Zero Trust is about the conditions inside the perimeter; BeyondCorp is about ingress through the perimeter. Things may be wide open on the interior side of the proxy. Or things may be locked down tight even inside the VPN.
I would think of BeyondCorp as end users accessing services through an application-layer perimeter from a public network, instead of directly from a private network.
The network where the services actually sit becomes, in effect, even more private.
