Why YAIBA: NINJA GAIDEN Z is considered bundled?

Could it be that it was discounted at 90%? I know heavily discounted games are counted as bundled, but don't know at exactly what %.

Probably because of this: https://www.steamgifts.com/discussion/y7dAZ/yaiba-ninja-gaiden-96-off

Maybe because it was widely used to abuse CV gain. Just a guess. Saw some people were giving away 5 copies at once with the only intention to get 150 CV at very low cost.

Probably because of many region restricted GAs to Russia/Turkey/Argentina when the game was on sale for well over 90% off in USD terms in those countries.

The game was 90% off on Steam on Mar 5, 2020. The historical price charts on SteamDB show that it cost 49 ₽ / ₺4,9 / ARS$ 33 in those 3 countries' currencies. That's the equivalent of $0.55-$0.75 which is a ~98% discount. A similar sale occurred on Apr 24, 2021. The archive shows a lot of region restricted GAs popping up around those sale periods, often for multiple copies. The change to reduced value on Mar 5, 2020 was probably a way to counter what was considered CV abuse (Gaining $100 CV for $2).