"Container platform" seems pretty vague to me, PaaS means something I know right away.
I mean, k8s is a container platform too isn't it ? But you'll need to build what we called a PaaS on top of it yourself (or use something like Kelproject, OpenShift ...)
PaaS isn't a verboten term or anything like that. But it turns some people off because it was most associated with services/products/projects that mostly focused on a simplified developer experience at the cost of flexibility.
k8s for me is a framework, OpenShit, Rancher, KelProject would be "distributions" of k8s, just like Linux kernel and distributions including it.
As a person who writes technical requirements and implementation document, it strikes to me when I'm asked to document implementation of a "SaaS" that there will be paid accounts and billing.
Maybe CapRover will provide paid accounts on managed servers in which case they would be creating a SaaS with their PaaS solution.
But again I'm not talking from a "managerial" perspective of the definitions, rather from a technical one. I suppose at this stage CapRover is trying to attract technical users rather than managerial ones (unless they have something to sell for cash but I didn't see it on their site or just missed it)
You're probably more likely to see OpenStack called a private cloud or on-prem cloud than "IaaS" these days. And OpenShift is usually called a Container Platform rather than a PaaS.