You seem adament on being offended by this OP, so just take it up with the school.
You have a rare 7 year old though who repeats verbatim what the teacher says.
You seem intent on the fact the word 'some' should have been included. 'Some' chinese eat dogs. But your child did not say the teacher said 'all'. If they had said ALL chinese eat dogs, you might have a point.
It was general statement. In china, where chinese people live, they eat dogs. and given your child is intelligent enough to remember exact word for word what a teacher said during the lesson, surely you would consider him intelligent enough to realise that obviously not ALL people of that nationality, in that country, eat the things they were dicussing.
Are you equally offended by other generic statements about food?
The italians eat pasta
The scottish eat haggis
The turkish eat goats
the french eat snails
The english eat fish and chips.
Are these racist too?
The actual fact is that people in china DO eat dogs. not all of them, as I'm sure not all italians eat pasta or all scots eat haggis. The fact it was considered derogatory in the past does not make it untrue today. It is a fact. Not racist. A fact.
And given the context of the actual discussion - what do people in other countries eat - I imagine the school was teaching the dc how diverse different foods are across different cultures. And knowing my 7yo, the grosser the better.
But take it up with the school, tell them they should not mention chinese people eat dogs in case your child does not understand it isn't ALL chinese people and also you don't want him to know that some do in case he repeats it and looks like a racist.
Honestly, if my 7 yo came home and said, he learnt today chinese people eat dogs, firstly i'd ask about the lesson and then I'd just say well yes some do, not everyone though, just like everyone in england does not eat chicken or brussel sprouts. 2 seconds to clear that shit up, yet here we are on page 10 over a teacher missing out the word 'some' or stating a fact you find uncomfortable.