I've been in US wilderness areas that were absolutely covered in frogs. As in areas 50 ft wide or larger. So I'd agree with you - could have been a completely n

I've been in US wilderness areas that were absolutely covered in frogs. As in areas 50 ft wide or larger. So I'd agree with you - could have been a completely natural occurrence - maybe a mudslide or some kind of toxic algae that killed them before Mother Nature covered them.