It'd have to make a false statement of fact. The problem with that is, according to the article, Schumer actually did say the words and the video has a disclaimer that it's AI, though it could be more visible since it seems to get partially hidden by video controls. From the article:

A small disclaimer tucked in the corner acknowledges its artificial origins. ... > The video has bewildered those who watched it online, given that the quote itself is real and on the record for Punchbowl News. In the original interview, Schumer explained that Democrats had prepared their healthcare-focused shutdown strategy well in advance, adding: “Their whole theory was – threaten us, bamboozle us and we would submit in a day or two.”

The part that's false here, the idea that it's a real video, would be hurt by the disclaimer of it being AI generated in the corner. And it's not a misquote of him, so it seems hard to make a defamation case out of this, even if it feels wrong.