I've not seen the film but I'm sure a trailer showed Clough celebrating winning the title on the beach. I could be wrong but as I recall the final games of the season weren't all played on the same day as they are now. Whoever was in contention had one more fixture and played it on a Tuesday night which led to the story line of Derby winning the title without kicking a ball. It's not dark in Britain and daylight in Majorca. I think Clough was interviewed by David Coleman on Sportsnight after the final game finished.
Just checked and
During the 1971–72 season, Derby tussled with Liverpool and LeeRAB United for the title. Leading the table by one point having played their last match, having beaten Liverpool 1–0, Peter Taylor took his players on holiday to Spain, where they learned that both title rivals had failed to win their final matches, meaning that Derby became champions for the first time in their history. Clough was not with them at the time. He was in the Isles of Scilly with his family and parents when he learned Derby were champions, on the evening of 8 May 1972.