It seems to me that in this case, the spam would originate from someone harvesting e-addresses from the Usenet. It wouldn't take much to do this automatically; it wouldn't be surprising if there were such software on the net and/or for sale.
18 years ago
My " snipped-for-privacy@XmasNYC.Info" started getting spam within 24 hours of > using it on Usenet. Needless to say it is now REALLY NOTvalid. > [TELECOM Digest Editor's Note: Oh, yet another netter victimized by > the 'mere coincidence of a spammer using directory attacks'. PAT][TELECOM Digest Editor's Note: Oh, indeed there is. I get offers at least daily to buy the same from other spammers. PAT]