Tested both entries (adapter & ethernet interface on monitor)
dmesg from thunderbolt display
http://dmesgd.nycbug.org/index.cgi?do=view&id=3185
dmesg snippet from gigabit adapter (mac address trimmed)
bge0: <Thunderbolt Ethernet, ASIC rev. 0x57766000> mem 0xacb00000-0xacb0ffff,0xacb10000-0xacb1ffff at device 0.0 on pci8
bge0: CHIP ID 0x57766000; ASIC REV 0x57766; CHIP REV 0x577660; PCI-E
miibus0: <MII bus> on bge0
bge0: Using defaults for TSO: 65518/35/2048
bge0: Ethernet address: 40:6c:8f:
Not sure if I should extend the man page to state that hot plug isn't supported on FreeBSD (like on OS X) hence device should be connected prior to system power up and removal should be avoided when system is live (system stays up if I recall correctly, but kernel freaks out that a bge interface just disappeared).