I don't think you got a satifactory answer. I too would like to know. I've often wondered about 'credits from other sources', and have never completely understood it. (BTW, this income is not included your credit income, so it alone doesn't explain why you had the best income.)
Sometimes I've seen players with huge amounts of 'other income' in the opening minutes. And I don't know what it is! My only explanation is that they are scuttling stuff - or changing their minds about stuff they ordered to build, and then cancelling it.
Its NOT feed. I wish there was a graph that showed feed. But there isn't. Even tho some players say there is! ("I'm gonna look at the end of the game to see how much you were fed"...).
Early game it could be Sova Embargo. That's about it (early game). Late game it could be TEC Perasive Economy. Or Evacuator Drain Planet. Or the Vasari tier 3 tech that allows Cap ships to collect 5/10/15% 'salvage' from destroyed structures & Cap ships. But I don't know what else.