Whether either scene was in the book, neither was out of character. He was someone with ambitions that were going to be crushed, consequently a lot of anger and developing alcoholism. Neither the anger that led to the dump bucket scene, nor the depression on realizing that his book would never be published and he had lost a relationship with a woman he cared for, his ex-wife was happily remarried, etc., that led him to drinking his prized wine in a way that devalued it, seemed unlikely at all. The only thing I don't understand about the movie was Miles' belief that California Pinot Noir was somehow better than California Merlot