bug#31062: 26.0.91; warning on UTF-8 encoding of unibyte text

[Charles A. Roelli]

(This test case assumes a locale-coding-system of utf-8-unix, and
LANG: en_GB.UTF-8 or anything similar.)

emacs -q
C-x b test RET
M-: (insert-byte 195 1) RET
M-: (insert-byte 188 1) RET     > buffer text should look like \303\274
C-x C-s /tmp/foo RET            > the path is irrelevant

There's this warning:

These default coding systems were tried to encode text
in the buffer ‘test’:
  (utf-8-unix (1 . 4194243) (2 . 4194236))
However, each of them encountered characters it couldn’t encode:
  utf-8-unix cannot encode these: \303 \274

Is the text "(1 . 4194243) (2 . 4194236)" useful here?  It looks like
it's there by accident.  If it is helpful, could someone please
explain what it means?