Routers PE1 and PE2 in the diagram exchange MP-BGP route updates that carry the route-target...

EVPN (Ethernet VPN) VPLS (Virtual Private LAN Service) uses MP-BGP to exchange reachability information.

When PE1 and PE2 exchange MP-BGP route updates for VPLS 300, the addressing information included pertains to EVPN MAC addresses.

This is because EVPN uses MAC address learning over MP-BGP to provide the Layer 2 VPN service.

References:

Nokia Border Gateway Protocol Fundamentals documentation, Section 8.3 on EVPN route updates and MAC address learning.