fontconfig is the library responsible for indexing and looking up fonts (e.g. by name - note that most software doesn't specify fonts by file name but rather by font name)

If fontconfig fails to stat() a font file, it presumably aborts trying to record any information about that font file. Notably, it doesn't know what the font file's actual font name is. If all fonts fail due to stat(), no information will be available about any font. fontconfig has multiple levels of fallback (e.g. "similar" fonts first), but in this case since nothing is known about any font you just get whatever font happens to be first in the list of all fonts.