It is very common for embedded vendors, when changing the underlying OS, to try to keep the UI unchanged. Once upon a time, every IBM mainframe contained a PC running OS/2, which was used to perform system maintenance functions such as startup and shutdown, hardware configuration changes, OS installation, etc. At some point, IBM decided to get rid of OS/2 and replace it with a HTTP server running on x86 Linux – but they had the webapp emulate the OS/2 UI look, so it still looked like OS/2 even though it was now a webapp. (I believe more recently they've refreshed the UI so it doesn't look like OS/2 any more.) So it wouldn't surprise me if, when they migrated from TOPS-20 (or possibly it was their own custom PDP-10 OS) to BSD, they kept the CLI as unchanged as possible.

It also wouldn't be the first kind a Unix application has used a TOPS-20 inspired interface. The most famous example of that is Kermit. Columbia MM is another.