There are currently at least 3 ways to refer to a GPG key: short key ID (last 8 hex digits of fingerprint), long key ID (last 16 hex digits) and full fingerprint. The short key ID used to be popular, and since 5 years it is known that it is computationally easy to generate a GnuPG key with an arbitrary short key id.
LWN.net wrote in June 3, 2016:
Gunnar Wolf urges developers to stop using "short" PGP key IDs as soon as possible. The impetus for the advice originates with Debian's Enrico Zini, who recently found two keys sharing the same short ID in the wild.
After contacted the owner, it turned out that one of the keys is a fake. In addition, labelled same names, emails, and even signatures created by more fake keys. Weeks later, more developers found their fake "mirror" keys on the keyserver, including the PGP Global Directory Verification Key. Gunnar Wolf wrote:
We don't know who is behind this, or what his purpose is. We just know this looks very evil.
Now, a fake key (fake: 0x6211aa3b00411886, real: 0x79be3e4300411886) of Linus Torvalds was found in the wild, scroll the page and you'll two of them. It looked like that every single key from the Linux kernel community have been forged successfully, another example is Greg Kroah-Hartman (fake:0x27365dea6092693e, real: 0x38dbbdc86092693e). LWN reader "rmayr" commented:
so it seems somebody is actually constructing a database of fake keypairs with "well-known" short IDs. Something is going on here...