I understand that "the python programming language" probably doesn't involve snakes. On the other hand, "the TeXmacs math typesetting software" doesn't obviously not involve LaTeX and isn't obviously not for emacs.
It is a bit discomforting seeing that discussion in hackernews just remain at the level of "bad choice of name, btw!" without no technical insights. I would have expected more sensible reactions. TeX and Emacs were initial inspirations to TeXmacs (which has been written in the '90). As such they indeed inform some of the design choices, that said TeXmacs do not conform to them. The Emacs legacy is however very clear: all the editor behaviour is re-programmable in Scheme, from keybindings to menus, to the graphics editor (see here a recent example http://forum.texmacs.cn/t/why-not-draw-circle-by-center-and-...). As for the TeX legacy, TeXmacs actually improves on it by defining a document format while retaining the power of creating user defined macros, it also allows scheme code to be called from macros, since its beginning, 20+ years before LuaTeX. An overview of TeXmacs design can be found here: https://texmacs.github.io/notes/docs/overview.html . I think people nowadays are more used to programs which are epsilon changes over existing systems, repackaged with brand new names. That is why TeXmacs could be puzzling at first. Does not fit usual categories. Maybe this says something of the current trends in (free)software design.
