Tolkien may not have been from Yorkshire, and in contrast to davem I reckon he was quite pleased about that - he did have a fondness for Lancashire's green and verdant valleys - but he would have well known the essential difference between lunch and dinner. This is in the very blood of the English, class is of vital importance to us, to none more so than the eternally anxious middle classes.
Note how Tolkien makes play of a Lancastrian working class term for dinner -
baggin becomes Baggins, a witty name for a Hobbit obsessed with his grub. Rather like snap this word comes from the fact that the working man's main meal of the day was carried off to the field or foundry in a bag.
If you think the use of 'lunch', 'dinner' and other terms amongst Hobbits is entirely casual on Tolkien's behalf you are sorely mistaken. He was an Englishman, keenly aware of class and language and how they are interlinked, as shown in his work; in The Shire there is much satire on the British way of life - cast that subtlety aside at your peril
