That's actually really misleading. A system like siri is split up into different parts:

-- speech to text

-- natural language understanding ( entity recognition, intent classification, entity resolution)

-- language generation and speech to text

It sounds like what they're saying is that DNNs are used for their speech recognition (speech is split into acoustic and language modeling, and DNN speech models have been state-of-the-art for about 4 years). It's kinda a "so what?" that they were using DNNs for their acoustic models, and nothing to do with the interesting parts of the system.

If they were using DNNs for their NLU system back then I'd be kinda surprised.