I saw his YouTube video here: https://m.youtube.com/watch?v=qzpZQe7JT-o

One of the things I like about it is he had to create a little front end to display the game, mirroring actual COBOL practice. Until the 80s or so, COBOL didn't support meaningful terminal I/O in its own right; it was all batch. If you were a mainframe dev and wanted to do terminal interaction, you either had to write your own routines for that in mainframe assembly or use something like CICS, IBM's application server which provided its own terminal handling and transactional database routines accessible through a language extension which got swizzled into regular COBOL by a preprocessor. Creating a layer outside of COBOL to do the things COBOL was deficient in, and using COBOL's regular I/O to communicate with it, is peak mainframe-era engineering.

Other solutions to the same problem existed; there was one called InterComm, which lacked the preprocessor and required you to reserve a shared area of memory and write messages to InterComm directly into it. These days there's KICKS, an open source library API-compatible with CICS, aimed at the sort of person who faffs about with old software on Hercules.