If you run the LXD snap, then you can have a look at
/var/snap/lxd/common/lxd/ (for the DEB LXD package, it is elsewhere in /var/...).
In there, you can get a lot of info:
$ cat /var/snap/lxd/common/lxd/networks/lxdbr0/dnsmasq.hosts/c1
$ cat /var/snap/lxd/common/lxd/networks/lxdbr0/dnsmasq.hosts/c2
Here it shows you what DNSMASQ (the one for LXD) thinks about the MAC Address of the containers.
In /var/snap/lxd/common/lxd/logs/ you can find the LXD logs, and also individual logs per container.
A real physical network interface has a proper, unique and defined MAC address. On the contrary, a virtual network interface (like those in containers) has a 00:16:3e:??:??:?? MAC address that is randomly generated when the container image is instantiated. It keeps the first part (00:16:3e) so that it is distinguishable from other interfaces.
For your case, if you want to delve deeper, you can have a look at the logs.