If I had to guess he setup VLAN’s on his current firewall, then he setup the VLAN networks on the xcp-ng pool for both VLAN networks. Then on the pfsense VM he set the interfaces to their respected VLAN.
Note: You’ll want 3 NIC’s total and your 3rd NIC can be a private network if you only want to have VM’s connected to that network for testing purposes. You could bind the 3rd NIC to a physical NIC if you wanted though.