Perhaps it wasn’t their own mental model of the landscape at all, but just what they considered to be the most expedient way of getting the message across in terms customers would understand.

Hypothetical analogy: if I were describing my very-first-ever PaaS service, to competitors who’d only ever heard of IaaS services — and this wasn’t the point of the conversation (i.e. I wasn’t trying to sell them on the benefits of PaaS), but rather just a supporting statement to talking about how we do/don’t offer an IaaS feature, because we’re a PaaS — then I’d probably describe my PaaS by analogy to some popular IaaS that has a feature-set closest to a PaaS.

In my own mental model, I have a separate node for “PaaS”; but if I know that the people I’m communicating with don’t — and teaching them what a PaaS is would take time away from the real topic we’re trying to focus on — then I’m going to describe my PaaS provider as “basically like $foo IaaS provider” when talking about how it has the same feature X. To them.