Biff's view of the past, as indicated in the flashbacks, relates directly to the theme of "the tragedy of the dysfunctional family".
The word "indicated" is appropriate here because these flashbacks do not serve to actually articulate Biff's views, but rather to point to his experiences and to imply an emotional response. Biff is depicted as a petty thief full of arrogance and a sense of exceptionalism and entitlement. Later, he is shown discovering Willy's dalliance with another woman outside his marriage.
Each of these scenes feature Willy shaping Biff's experiences in negative ways. While Biff was happy to be praised by Willy, he was also subject to a tendency to think of himself in an exaggerated way. His arrogance was a result of Willy's instruction.
Biff's disillusion is also a direct result of Willy's affair, which is a great betrayal for Biff. In this act Willy betrays Biff's notion of who Willy is (or is supposed to be) and shows him to be a fraud. As Biff was working to please his father and to emulate him, this betrayal comes as a huge blow to the boy. His life is turned by the event.
These flashbacks indicate Biff's conflicts and in doing so articulate the theme of "the tragedy of the disfunctional family".