Or maybe I'm totally wrong here - what differenciates between a web application and a website?
Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. That is, a website can plausibly consist of a static content repository that's dealt out to all visitors, while a web application depends on interaction and requires programmatic user input and data processing.
While modern architectures incorporate heavy client side processing.
It does not become a webapp It's like whisky and scotch, all web apps are web site, but not all web sites are web app.