In absolute terms it's not hard to believe (despite tiny sample size in the tweet) given the rise in popularity of seltzers and other low ABV drinks in the past 2-3 years. But in share of craft as % of the overall beer market? I suspect it's stable or even increasing given they're becoming more mainstream (albeit not sure if some original craft brands still qualify now that they're so dominant).
Seems like it could also be inflation related, where people are substituting less expensive macrobrews for more expensive craft brews.