In my dialect of English, the midday meal is usually referred to as dinner or lunch (depending on the size) and supper is the evening meal.
Thus my grandfather would say "Christmas is a hot dinner, a cold supper, and then a memory" and if one were to say, "Let's stop some place where we can get dinner and not just a lunch" makes perfect sense. It means lets stop somewhere we can have a sit-down meal rather than a fast food restaurant where we'll just have a burger and fries.
Now if this was just a case of the dialect being so different from Standard English as it is unique to the dialect (such as directly meaning soon rather than straight ahead), "We'll go directly." or an archaism that has been preserved in the dialect (such as holp for the past tense of help) then I wouldn't bother to mention it, but according to several sources, dinner still retains the meaning of the midday meal.
From the Oxford Dictionary of English:
"dinner, n., the main meal of the day taken either around midday or evening."
And Webster's Dictionary for English Learner attaches this usage note to "dinner":
Most Americans have dinner in the evening, although if the main meal of the day is served in the afternoon it is also referred to as dinner.