The difference is that Biden has markedly declined from previous performances. He spent most of that night stumbling, mumbling, and struggling to speak clearly, none of which is his stutter, because a stutter is a very specific speech impediment. He was downright difficult to understand on average, and flat out unintelligible at worst. Even when he got riled up, like with the losers and suckers remark, it sounded like he was having trouble forming word sounds accurately, like he has dysarthria. Even in carefully curated campaign material, like asking for donations, he sounds out of breath and like he’s struggling to speak clearly.