My guess is that it is a resource fork based font.
Resource forks are from the macOS Classic (pre MacOS X) days. A file could consist of two forks: data fork and resource fork. The data fork is where data would normally be stored while the resource fork would be where resources such as code, menus, icons, fonts etc… would be stored in a structured format.
The reason why those apps aren’t showing anything when opening the file is because they will only be loading the data.
Resource forks were abandoned when MacOS X was released so there isn’t much out there today that works with them.
The MBS plugin has functions to read the resource fork data.
I have read that you can open the resource fork by appending the following to the file path but it’s not something I’ve tried personally.
/…namedfork/rsrc