OK, you must mean the Rubin Report segment. He didn't say all Left is regressive, just some of it.
Laced into this typical type of generalized ranting, the snake oil guy often uses the tactic of taking a moment to step back and admit that he is not talking about the entire [
group being attacked,] but it's just an empty attempt to claim reason. But even after claiming reason, he continues talking about an extreme while attributing that behavior to the left as a whole.
So while you are technically accurate when you say, "But... but he said he wasn't talking about the entire group," the fact is he continues to refer to the entire group as members of the extreme, and his rhetoric doesn't support his vacuous claim.
This is a common political tactic. It's also used by some Democrats against Republicans, but not quite as often. Either way, used by the right or the left, it's a fallacy, acceptable as a tool for misleading propaganda, but not much else.