Seems fishy to me. How can a more complex device (ICE + EV) be more reliable than a pure ICE or EV? Also seems like a crap website, their chart show 79% more problems as red and then 26% fever as green.
Because modern ICE cars have freaking overgrown snowmobile transmissions, and a hybrid drivetrain can replace that entirely.
A hybrid can be simpler than an ICE car (by eliminating the transmission and allowing the engine to be power-banded) and cheaper than an EV (because a 10x size battery is more than the cost of the engine and generator).
Most mechanical stresses in the drivetrain are transient and happen in the transmission. In the engine, they happen in the "out of band" power regimes -- very low and very high RPM.
The hybrid moves those transient "stresses," and the imparted maintenance thereof, into the electrical system. The engine never sees them.
This unlocks additional efficiencies. For example, the Prius uses the more fuel efficient Atkinson cycle engine. This is not possible in a standard car, because it cannot provide enough power in those transient regimes. You also get things like regenerative braking which help prolong brake life.
And, there's probably a bit of selection bias as well. I could see that the type of someone who buys a Prius is the type to not thrash it. That probably makes it appear more reliable in the statistics.
A hybrid can be simpler than an ICE car (by eliminating the transmission and allowing the engine to be power-banded) and cheaper than an EV (because a 10x size battery is more than the cost of the engine and generator).