The money was wrapped up in the newspaper that George’s brother thrust into Potter’s hands. The uncle was absent minded not a drunk. The newspaper had a headline about George’s brother returning home a war hero. The uncle was taunting Potter about the headline.
While he wasn’t drunk then, his brain probably was helped along by a lifetime of going to far into tipsy.
When George thinks his life is over because of his uncle, he lays into him for everything. And to be fair, were his uncle a more capable man, George wouldn’t have needed to take over the business.