Is soy yogurt considered a fermented food?
Yes, in this context cultured and fermented mean the same thing.  The bacterial culture ferments the food product it consumes, converting sugars into acids (or alcohols).

Soy yogurt is a soy milk product inoculated with the same type of culture used to create yogurt.  Given that lactobacillus is well adapted for milk, it is amazing that this process actually works effectively and at a commercial scale.