I personally believe the spawn was programmed, and not something he did manually as you suggested.
Halloween scythes are not exactly in the same boat since you only could obtain one, so the system did change throughout 2002-2003.
Edit: I think Easter eggs and pumpkins had the same spawn system as Santas:
"
The drop occurred all around Gielinor on 31 October 2001, marking the 2001 Hallowe'en event. During the Hallowe'en event of 2001, pumpkins were found scattered around various towns and areas at different times during the day."
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