Ben grew up in Hong Kong, so understands Cantonese but ironically doesn’t speak it. He’s a Chinese language (Mandarin) and history scholar and that’s why he’s speaks in formal Beijing Mandarin.
You’re right about Carmen. She moved to Australia at a young age and that’s probably where she picked up her ‘accent’. The most telling is that she says gwei lo instead of gwai lo.
He’s not sure. He’s divorced and came across them while unpacking a box.
This reminds me of people getting hanzi or kanji tattoos without regard to what they mean, because they look good togeher, especially when combined (see my above post about ‘baka’ / ‘red deer’ above. 
It looks like the writing is below the glaze, is that correct?
If possible, post some pics of the front of the plates, which may help determine it’s origin, Chinese or Japanese. It seems it may be an attempt to give it a Japanese origin, when it really isn’t.
for clarification, that kanji is used in Japanese but just not alone like that.
Is it akin to a grammatical error, e.g. there instead of their? Or more like a non-native speaker may use there instead they’re? As suggested, would it be something that would make sense to a someone trying to spoof “Made in Japan”, not knowing the correct (Japanese) kanji and instead using hanzi that expresses the same idea?
Writing” “there” for “their” is a spelling mistake and not a grammatical error.
There isn’t an exact equivalence in English for the error they made, but possibly a “spelling” mistake. Using the wrong character as both 製 and 造 mean “make.”
Hell hath no fury like an angry 12-year-old.
Reported.