One of my muscadine vines produced very sour grapes this year.

There are three growing on an arbor, all black, and every year (over 6 years now) produce buckets of very sweet black muscadines.

This year one of the vines has fruits that are smaller than usual, but there are more of them and they are clustered together - and sour.

There was a bed of vegetables planted very close to the base of that particular vine so it recieved more water and nutrition that it has in the past - could this have caused the sour grapes?