Correct English grammar, but different Ukrainian sentence. That would be "Чий цей обід?"

It is incorrect, yes. The right way of writing that is "Whose lunch is this?"

So... At least we're sure breakfast is breakfast :') But then:

Lunch so far is just the midday meal, so обід.

Dinner used to be what we call lunch before, or simply the second meal of the day (so обід), but then it slowly got pushed to the evening it became the evening meal (so вечеря)

Supper is the old word for dinner (so вечеря).

I think it's like this.