I really have to remember dinner and lunch are not considered the same thing here. I get it wrong every time.
Unfortunately, it's gonna be the same in the Russian course. Different varieties of English think differently about what toilet, dinner and pants are, so you should stick to something consistently where two varieties contradict each other. Floor numbers are also a pain in the guts.
To say it differently, «обід» is either lunch or dinner but they cannot both be correct, unless most English speakers in the world think these two are the same meal (which is not the case). Similarly, while some people call a 4th floor what others consider the 5th floor, no person in the world thinks that 4th and 5th floors are the same floor of the bulding.
So in Ukrainian are lunch and dinner basically the same meal? I know that if you want to say "supper" the word is Вечеря.
I don't think there's any confusion in Ukrainian, as far as I'm aware обід is the middle of the day meal and вечеря is the evening meal.
My confusion just comes from the English side, as where I'm from dinner/lunch is the mid day meal and tea is the evening meal, so I have to pay more attention to get the English right or I automatically write обід = dinner (meaning the mid day meal to me, but obviously means the evening meal on duolingo).
It is further confused by which day of the week it is. Sunday dinner is somewhere between 12 and 5, depending on the tradition in a family or area, although some people call it Sunday lunch! But dinner can be an evening meal, particularly if you are going out for dinner. Also people often ask 'what's for dinner?' if they get back for a cooked meal at lunchtime. in Yorkshire, it is often called dinner time at lunch time and tea is the evening meal; but if you grab a sandwich at mid-day, then it's called lunch! There is much debate about this subject. It's all really rather confusing.
However, most people seem to agree that dinner is the main meal of the day, irrespective of whether it is at 12 o'clock mid-day or 8 o'clock in the evening. This does not help people learning English!