From a Cox VP of Digital Strategy's blog post:

"Our technology is on the cutting edge of voice data processing. We can identify buyers based on casual conversations in real time. It may seem like black magic, but it's not-it's AI. The growing ability to access microphone data on devices like smartphones and tablets enables our technology partner to aggregate and analyze voice data during pre-purchase conversations."

IMO, the smoking gun here is their partner ingesting and analyzing the voice data.