I can only tell you a bit about my experiences with tomatillos (other climate, circumstances,....). First of all, a ground cherry (physalis pruinosa) is not the same as tomatillo (physalis ixocarpa). Ground cherries are sweet tasting small berries, un to max 2 cms big (that's already big!), they are in fact a smaller version of physalis peruviana. Ground cherries are generally speaking self-pollinating, and will certainly never cross with tomatillos. Tomatillos however aren't self-pollinating, meaning you need to have at least two plants of one variety. Strictly speaking, because they need this other pollinating plant, they are indeed hybrids, but so are lots of cabbages or allium. If tomatoes get pollinated from insects, even within the same variety, they are hybrids, but if this pollination happens within the same variety, you won't notice a thing when you grow out the seeds.
Now , for isolation distances. I have about the same isolation distance you have (100 ft), I've been testing for a few years, and they do not cross over here. But I have lots of other flowering plants in between the tomatillos. Especially bigger plants wearing lots of attractive flowers can play a major role. And , of course, the activity of insects, the insect types,....
Try it out, re-sow the seeds the next year and see what has happened
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