For jacket they are speaking of a sports coat or suit jacket. Men will be wearing slacks, button up dress shirt and jacket/sports coat, most men will be wearing a tie also.
Women will be in a range from cocktail dresses to dress slacks with a dressy top. I always wear a dress and heels. Last time I ate here I was cold so they brought me a cashmere shawl to use while I dined.
This is a very formal dinner. Part of the enjoyment is dressing up to match the quality of service/food you will experience here.
Got the reservation then went to try on the suit the jacket seemed fine then I saw it...Moth holes all over the pants and jacket then I went to put on the pants (its been a while) strained for about 3 min before I accepted I have gained weight (a healthy amount) but it was too funny! Had to call and cancel the guy says "Didn't I just talk to you?" I explained and he said everything was ok.
Man what an experiance to have day before departure!
Oh No! V&A's has a limited inventory of men's jackets to loan (at least as of the last time I was there). Maybe you could call and ask, and get the reservation back. It is truly a wonderful experience.
Have you also considered Bistro de Paris upstairs in France at Epcot. It's not as fancy (or quite as pricey) as V&A but is still a very nice grownup type of place. It does not require a jacket, nice slacks would be fine.
Sorry about the waist expansion. I have that problem every time I go to WDW.