Earlier quoted context omitted.
That Wikipedia section needs a rewrite. It does mention that that usage is a class marker but then conflates it with the pastry-and-tea afternoon snack practice of upper classes. They are two radically disjoint uses. The origin of the “tea” being the term for evening meal are pretty well attested to lie the poverty of the English lower classes who could not afford much more than a cup of tea in the evening. I grew up…
I'd never heard of this before. Growing up in rural Scotland, meals were always "Breakfast", "Dinner" and "Tea". There was sometimes confusion with other people over whether dinner was a midday or evening meal, but I'd never thought much of it until now.
At some point dinner transitioned to lunch and teatime to dinner for us.