I wonder of the white stuff is some kind of manna, which can be fungal or crystallised honeydew secreted by certain types of aphids, Better that you kept your toddler out of the cats, especially the large one with yellow flowers. Aptly named Ferocactus, they draw blood with ease
Maybe it was just a super infested cactus with mold. Unless someone put a fake thing in there to intrigue visitors lol. I grew up in the desert with all these types of cacti and have been pierced by a number of different ones, the cholla was the worst.
Chollas are invasive here so fortunately they aren't cultivated. One look at those makes my skin crawl
I have seen the cholla wood go for lots of money in tourist shops and on etsy, if they went to AZ they could make a fortune harvesting it and selling it. Though you would need body armor to avoid the spikes, then who knows how they could be able to rot the skin off quickly for harvest.