What that refers to is the shape of the "O"ring, and that it has turned into a "C"ring basically and ressembles Pac-man's shape.
I worked some 25+ years in the Injection Molding field, lots of O-rings on one of those machines. I've seen many o-rings blow in that manner. And for the most part, yes,, they get blown in, not sucked in.
On the intake/supply side of the pump, yes,, they do get sucked in. But on the pressure side of the system, they get blown in from system pressure.
The o-rings sit in a cavity and do not have an internal support. O-ring seal is made by the squish of the mating surfaces and relies on system pressure to help make the seal from the fluid putting pressure on it in a radial pattern outwards.
Heat is one major enemy of o-rings, time is another. Combine the two and problems will arise.
As the o-rings age they lose thier flexibility comprimizing the seal. When that happens, system pressure can migrate to the outter side of the o-ring. With no internal support of the o-ring, fluid pressure will push inwards on the oring, causing it to fail.
Doesn't matter if system pressure is 10 PSI or 2,500 PSI or if it's oil, air, water.
The reinforced o-ring basically keeps the o-ring from collapsing in on itself if/when the seal is comprimized.
If there was a U-shaped channel vs the flat recess for the o-ring to sit in, seal would be mantained better/longer.
Just my .02...