"Bridge firewalling registered"

Below is /var/log/messages from a ER-X-SFP at a client site.

It rebooted on 8/15.

Then on Aug 17, the first and only msg after the boot sequence is a line with:

"Bridge firewalling registered"

$ cat /var/log/messages
Aug 15 06:25:11 PWTW01-BLDG1-router rsyslogd: set SCM_CREDENTIALS failed on '/dev/log': Protocol not available
Aug 15 06:25:11 PWTW01-BLDG1-router kernel: Linux version 3.10.14-UBNT (root@edgeos-builder2) (gcc version 4.6.3 (Buildroot 2012.11.1) ) #1 SMP Sat May 28 09:48:10 PDT 2016
Aug 15 06:25:11 PWTW01-BLDG1-router kernel: 
Aug 15 06:25:11 PWTW01-BLDG1-router kernel: The CPU feqenuce set to 880 MHz
Aug 15 06:25:11 PWTW01-BLDG1-router kernel: GCMP present
Aug 15 06:25:11 PWTW01-BLDG1-router kernel: Zone ranges:
Aug 15 06:25:11 PWTW01-BLDG1-router kernel:  Normal   [mem 0x00000000-0x0fffffff]
Aug 15 06:25:11 PWTW01-BLDG1-router kernel: Movable zone start for each node
[snip]
Aug 15 06:26:09 PWTW01-BLDG1-router kernel: ESW: Link Status Changed - Port0 Link Down
Aug 15 06:26:11 PWTW01-BLDG1-router kernel: ESW: Link Status Changed - Port0 Link UP
Aug 15 06:26:13 PWTW01-BLDG1-router kernel: ESW: Link Status Changed - Port0 Link Down
Aug 15 06:26:15 PWTW01-BLDG1-router kernel: ESW: Link Status Changed - Port0 Link UP
Aug 17 14:14:10 PWTW01-BLDG1-router kernel: Bridge firewalling registered

'last' shows no logins from when the unit reboot until today (8/19). 

Both 'sudo iptables -n -L' and 'sudo ebtables -L' show empty rules set which is correct because I never defined any filewall rules.

So,

1) What does "Bridge firewalling registered" mean? (I'm guessing that it means that ebtables was started...)

2) What would cause the system to generate this log message when, as far as I can tell, no one accessed the unit or made any config changes? (I'm the only one with access, unless my network has been compromised.)

Thanks

Mark