This is a "loaded" statement...primers, in proper use do go off from impact but not just with impact, they can also go off if the anvil is scratched across the priming compound the same as striking a wood match.
I have had 4 primers detonate in progressive press's, two in a Lee Loadmaster and 2 in a Dillon 650 . The ones in the Loadmaster happened when the primers did a 1/2 flip in the plastic primer feed slide (very common occurrence in the Loadmaster) and were crushed a bit when I unknowingly tried to seat them sideways...no "impact" at all just the regular primer feed pressure. The two in the Dillon happened when the primers were still in the primer feed plate, not even up to the primer seating position yet. I suspect the primer anvil was slightly "proud" from what a well formed primer should have been and when the feed plate rotated, that anvil hooked on an edge in the mounting casting, scraped on the priming compound and lit like a match...no impact here neither....just very loud f#@$'n "bang" when you least expect or want it...It will get your undivided attention immediately!!
I want to add that I have had many primers feed sideways in that Loadmaster and not detonate so they dont always do that...but some do.