From the Legends perspective, I see it as backlash from events depicted in Rebel DawnRebel Dawn, the depiction of Bria's (Han's love interest) actions towards Lando, confiscating his property in the name of the Rebel Alliance. Defaced and being branded a traitor back on Nar Shaddaa, Lando refuses to believe Han was not involved in the swindle, and punches his former friend in the jaw.
I like this perspective. Changed your source to be inline with your description.