Great job
It's really simple, it's a container containing a virtual os, which runs a browser and a webserver to run the app. The app connects to several external api services to do it's thing.
It's like, really simple!
I‘m very scared that this might actually be the case in some apps out there.
If they're running a virtual OS in a container, they're doing it very wrong. Containers and VMs are quite different, even on a Windows host.