I would imagine the biscuits simply weigh more than 30g.
Looking at the Tesco site a 540g box contains 24 so that makes them 22.5g each so two would weigh 45g - a LOT more than 30g!
Anyway, the Weetabix choc are not listed as a HEX & 2 syns online any more, so technically you shouldn't be having them anyway unless you syn the lot

(There are plenty of threads on here about it if you do a search)