... could be caused by cheating

[Endoperez]

There are (or were) few cases in which player might accidentally cause extra gold for himself. As lch said in the first page: "Most usually this is an unexpected thing like removing units from building queues of forts that have been taken over."

Also, having high-enough Alchemy bonus and converting gems to gold used to produce a cheating message. That was quite annoying, because a Master Alchemist pretender with a Philosopher's Stone triggered it, and even then it's the gems-to-gold ratio is pretty low.

I don't know anything that would cause it in the early game, though.