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.

Lynx doesn't look very Unixy too.

Its amusing, early XKL documentation called it "router style user interface" so while it might have been PDP-10 under the surface, it looked like a Cisco Router from the get go, which makes sense considering the market intended for.

This has more to do with Cisco's IOS command line being a direct clone of the TOPS-20 "Exec" than XKL attempting to clone Cisco's interface.

The first time I sat down at a TOPS-20 box, I could see the genetic similarity.

Also, I was not presuming XKL cloned Cisco - considering the shared provenance of it all.