HoMM VII Haven Units – Haven faction units from the seventh installment of Heroes of Might and Magic.

I mentioned the sa render mod for GTA San Andreas, and no one had the source code for it.

We don't know what resources they had, what tools the developers left them with. I don't want to go into details now, and superficially comparing such things is meaningless. Maybe it's just a mod on some third-party engine, or maybe they used elements from the next game in the series (as far as I understand, Rockstar uses the same internal engine for GTA, constantly improving it).
In short, I don't know how it was done there. But, for example, I know how something similar was implemented for Jedi Academy. There, too, talented people added the display of a normal map; for this, the source code was required, which has been open source for a couple of years now. Only now, no one uses this feature because, unexpectedly, displaying normal maps requires models with these normal maps, which no one has made for this game yet.