You are right. The way to reproduce this issue (not related to mktexlsr)
is
(1) Install texlive-full and fonts-noto-cjk from experimental.
(2) Run lualatex with the below LaTeX source and have error
"Package fontspec Error: The font "NotoSerifCJKJPLight" cannot be found."
(3) Installation of fonts-noto-cjk-extra fixes the issue even though
no font from
fonts-noto-cjk-extra is used. XeLaTeX (with \usepackage[noto]{zxjafont}) and
uplatex (with \usepackage[unicode,noto-otc]{pxchfon}) produce the desired
PDF without fonts-noto-cjk-extra.