So far, it seems that CUPS is trying to connect to it via LPD, which I’ve specified in my pfSense rules, but it appears that the printer itself just rejects any traffic.
pfTop: Up State 1-4/4 (93), View: default, Order: bytes
PR DIR SRC DEST STATE AGE EXP PKTS BYTES
tcp In 10.1.0.10:1023 10.0.0.4:515 CLOSED:SYN_SENT 00:00:23 00:00:23 5 300
tcp Out 10.1.0.10:1023 10.0.0.4:515 SYN_SENT:CLOSED 00:00:23 00:00:23 5 300
udp In 10.1.0.10:38505 10.0.0.4:161 NO_TRAFFIC:SINGLE 00:00:32 00:00:00 2 142
udp Out 10.1.0.10:38505 10.0.0.4:161 SINGLE:NO_TRAFFIC 00:00:32 00:00:00 2 142