It would be more helpful if you posted the whole reaction.
If I had to guess, the ether at carbon 1 on the right-side sugar is also hydrolyzed.
You just need to track the water. There is a R-O-CH3 at the start and then you add in H2O to produce R-OH and CH3OH.
It is likely just a secondary hydrolysis reaction that is occurring in addition to the separation of the sugar linkage.