[g051051]

Most likely they had a web front end that talks to the legacy system. Very common in big companies.

It was probably developed very quickly, possibly outsourced, and just stuck in front of the older system with minimal re-engineering.

Many years ago, I worked on a system that put an X Windows front end in front of a mainframe app that used a 3270 emulator to interact with parts of the legacy app. I imagine this is somewhat similar.