winter peas?

In my initial shopping spree of seeds for my first ever time trying to garden (a couple years ago now), I got some peas from a local seed producer who maintains their own landrace. The packet instructions said to plant in spring or fall, and the rest of the description seemed to imply (although didn't outright state) that I should expect a harvest later in the same season I planted them. The ones I planted in spring did indeed produce seed in early summer, and then died in the midsummer heat. Then I planted more in fall, and perhaps I planted them too late but they didn't even flower before I left for the winter. But to my surprise, a few plants were still alive when I came back in spring, and they proceeded to grow and produce seed in early summer. I thought this might be a fluke, maybe a warmer winter than usual, but then last fall I planted some of the harvested peas along with more from the original packet, and sure enough this spring they were still alive. Some of them looked like they died all the way back to the roots and re-sprouted, but all are currently well ahead of any of the peas I planted fresh this spring.

I hadn't heard of overwintering peas in any of the research I had done, so I tried a bit of internet searching to see if this is something people do on purpose. All the results seem to refer to winter peas as a "cover crop" strategy, which to me implies that they're not actually intending to harvest any peas, just keeping some roots in the ground in between planting summer crops. And it might even imply that they expect these plants to die during the winter.

I've had trouble getting nearly anything to grow through the summer without (what seems to me) an excessive amount of watering, so I'm very interested in anything I can grow over winter instead. So far, that's pretty much just rye and, apparently, peas. The combination of those two has me rather excited because it would be a reasonable combination of crops to survive off of, if it ever comes to that.

So is this a normal thing? Have I stumbled across some incredible variety of super-peas, or is this just a thing that peas do but I failed to find anyone on the internet talking about it?