I might be wrong, but to produce a metastable Higgs, I believe you'd need a particle collision at that energy level, not just some random particles whizzing away from a supernova.
If 1020eV particles are relatively scarce, and mostly happen Out There, then collisions are relatively improbable and so will happen only infrequently. If the probability of producing a metastable Higgs from such a collision is also low1, then false vacuum collapse may simply not have happened yet in our Hubble volume.
It might have happened innumerable times outside our Hubble volume - we'll never know.
As others have pointed out, it might also have happened within our Hubble volume and simply not reached us yet. (I've seen sources that claim the expansion of the lower-vacuum-state bubble happens a bit slower than the speed of light, for some reason I can't recall; and if that's true we will be able to see its effects, though probably only briefly.)
Since the universe apparently still exists I'm going to go out on a limb and say either something was lost in translation or this isn't much of a threat.
The key word there is "apparently". All we can go on is what we perceive, and we very likely don't perceive more than a very small part of the universe.2
But it's not worth worrying about false vacuum collapse, for the simple reason that you can't do a damn thing about it before it happens, and you won't care afterward.
1I have no idea what the speculation on this topic says, and I can't be bothered to look it up, since I'm in no position to vet the material I find.
2It's unprovable whether there's anything outside our Hubble volume, for reasons that should be obvious, so this remains forever a cosmological hypothesis. Of course per the epistemological scandal so does everything else, ultimately.