There is a difference between them.
“Tea”, capitalized only when it comes at the beginning of a sentence or forms part of a proper name, is the leaf of the Camellia sinensis plant. Worthy of respect, tea is delicious. It may be served at a Tea, and in some places, Tea and tea are indeed the same thing.
“Tea”, capitalized whenever it is written, is the proper name of a steampunk event and an attitude. While tea may be one of the beverages at a Tea, perhaps even the primary beverage, a Tea does not have to have tea. It is the attitude and panache with which it is served that defines Tea. Tea is an interlude in the day, a civilized break. It can also be a meal. It is many things, and tea is but a small part of it.