It does not say that there was only one $600 transaction, only that a $600 transaction can barely buy a particular weapon. It says that they're structuring the payments to be small to avoid money laundering notice.
'Lim explained to a colleague that terrorists usually send “small sums” as “large sums constitute money laundering.” Lim’s colleague replied: “can barely buy an AK47 with 600 bucks.” And with regard to certain Binance customers, including customers from Russia, Lim acknowledged in a February 2020 chat: “Like come on. They are here for crime.'
We have no idea from this what sort of money laundering Hamas was doing on Binance, or if it was found ex-post, but we do know that at least one Binance employee thought they were using it for crime.