Sounds like he was looking at downloading a complete TeX Live distribution; XeTeX itself isn't anything like that size (by a couple orders of magnitude, at least).
"MacTeX installs TeX Live, which contains TeX, LaTeX, AMS-TeX, and virtually every TeX-related style file and font. [...] MacTeX also installs the GUI programs TeXShop, LaTeXiT, TeX Live Utility, and BibDesk. MacTeX installs Ghostscript, an open source version of Postscript."
Which is, as you say, considerably more than just "XeTeX".
(Also those are universal binaries containing both Intel and ARM versions which probably adds some heft.)
Heh, I remember when "universal binaries" meant "PowerPC and Intel". Different universes ….
I wonder what distro or editor he is using...