I don't think the fertilizer has anything to do with it: excess nitrogen stimulates a lot of leafy growth to the detriment of flowers and berries. But I have never seen it happen to vegetable, only ornametals.
There's actually a strain of San Marzano tomato called "Scatolone" (big box) in Italy which are specifically bred to be very "hollow" and almost as dry as bell peppers to be used in some dishes: the genetics of San Marzano are pretty weird and to make matters worse it seems the original strain introduced in 1926 went extinct in the early 60's as it was rapidly replaced by improved hybrids. I can only guess you are seeing some of the usual genetic weirdness associated with San Marzano, especially those coming from open pollinated seeds.
Here's a tip to force ripening before the first frosts: leave all plants on their supports and strip away all the leaves and the smallest berries. You should get your tomatos to ripen in 10 days at most (unless the weather turns really cold) and it will also slow down the spread of blights.
