Check this thread which pretty well describes different “personalities” of bridge in ROS.
Vlan ID 1 is a default PVID setting on all bridge ports. If bridge port is allowed to work with untagged frames (i.e. frame-types is set to anything but admit-only-vlan-tagged), then it will be automatically added as untagged port under /interface bridge vlan. In your case, those are ports BR1 and ether1 (the rest have pvid set to different values).