He didn't. "The only garbage I see is his supporter's" garbage, i.e, it's the possessive "'s". The clue here is 'is', singular. If he meant a group of people, he'd have said 'are', plural.
Anyway, Trump called the whole country a garbage can, so if you're so desperately offended by your misunderstanding of Biden's comments, I guess you're also pretty torn up about Trump's actual comments, right?
No, he didn't. Both the context and the grammar make it clear that my interpretation is correct. Even if you interpret it unsumpathetically, the inference that it's 'all' Trump supporters is something you've added.
Any Trump supporter pretending to be offended by what Biden didn't actually say is in any case a massive hypocrite, because Trump built his political career on being offensive. They can't turn around now and act all offended unless they also repudiate Trump.