One of the authors here! Impressed people picked this paper up so quickly. To clarify, KataGo does indeed take the rules as an input. KataGo was trained with Tromp-Taylor like rules, with some randomization. From section 2 of the KataGo paper:
"Self-play games used Tromp-Taylor rules [21] modified to not require capturing stones within pass-aliveterritory. “Ko”, “suicide”, and “komi” rules also varied from Tromp-Taylor randomly, and some
proportion of games were randomly played on smaller boards."
KataGo actually supports an impressive variety of different rules. We always used Tromp-Taylor in evaluation, in keeping with KataGo's evaluation versus ELF and Leela Zero (section 5.1 of above paper) and work in Computer Go in general.
I get these games might look a bit artificial to Go players, since humans don't usually play Tromp-Taylor. But we view our contribution not about some novel insight into Go (it's really not), but about the robustness of AI systems. KataGo was trained on Tromp-Taylor, so it shouldn't be exploitable under Tromp-Taylor: but it is.