The vendor name is not stored on the device, rather it is indicated only by the first three octets or OUI part of the MAC address which is either stored on the device, or in your case set up by software. Turning this back into a name on another computer which sees its traffic is done by the help of a local or network-sourced OUI lookup table.
Apparently the table your computer is consulting doesn't have an entry for the OUI 0xDE, 0xAD, 0xBE.
And that's not surprising as this is clearly a dummy value put in as a placeholder - read all 6 octets as if they were a word and you'll see it says "dead beef feed" - a variation on a classic magic "illegal" value.
Technically, this is actually a legal value for use on a local network as the 2's bit of the leading octet is turned on, indicating that it is a "locally administered" address, rather than one guaranteed to be unique in all the world as you would expect a proper piece of network hardware to have.
If you find the table your computer is doing OUI lookups in, you could add a DE:AD:BE entry to it.