A Judge of 30 years states, "all heroin dealers have guns".

I agree that the bald statement that "all heroin dealers have guns" is almost certainly untrue. But in response to the purported actual judge who was quoted as saying an urban heroin dealer that is not armed would be an anomaly. That statement would not be a logical fallacy. I think that judge was speaking from his experience on the bench. Since heroin is an illegal substance, making dealers subject to robbery and police action against them, they are highly likely to be armed to defend themselves and their inventory. My suspicion would be that the actual number of armed heroin dealers would be close to 100%. So I think the judge would be right in stating that an unarmed heroin dealer would be an anomaly. Does that prove that the gun was not planted? No. A jury would have to judge the credibility of the heroin dealer versus that of the police.

That is simply (with close to 100% probability) factually incorrect. I would assume the judge was using hyperbole in making that absolute statement.

I think this is in reference to the Lamar Smith case?

This is the judges quote:

"An urban heroin dealer not in possession of a firearm would be an anomaly," the judge wrote.

This was said in reference to the prosecutors claiming the gun was planted.