I'm the owner of the modem. I've found about this a couple of months back when I moved the modem to its own vlan and noticed the broadcast frames. I did some research into the author of the poem on Twitter (https://twitter.com/riojot/status/1268821579724541954), but nothing fruitful.
If anyone knows how the poem ended up in my modem, or even just what's ethertype 0x8300 all about, please comment!
The type 8300 is not a registered standard and the patent includes a payload description: "mac, port-info, vlan-info" (yes some is redundant to the headers, that is explicitly mentioned) and that doesn't fit the data. Maybe "Huawei compatible" in the meaning of "can be understood by their devices, but not exactly as patented by them". If a ring with a second such device is formed, it might respond with a different poem.
If anyone knows how the poem ended up in my modem, or even just what's ethertype 0x8300 all about, please comment!