I said and meant "traditional type of multihoming" and, more important in the previous sentence, "many hosts and sites that are multihomed in the traditional sense of advertising one set of endpoint addresses to the network and letting the routing system sort things out". That is, very specifically, one address per host, advertised to multiple ISPs/ networks/ paths and not "a chunk of PA IPv4 addresses from each upstream".
But it's the same thing -- the customer numbers some of their network with PA addresses from one provider and part of it with PA addresses from the other. Then the customer sends out traffic from both address blocks to both interfaces, and the upstreams can't tell whether an unknown address is a legit one from another provider or a malicious spoof.
I'm pretty sure this is right, having talked to ISPs about it in the context of why BCP38 is harder than you'd think.
R's, John