My definition is that they use tech as their differentiator and/or as their value proposition.

You can be a tech company and sell commodities, Amazon is an example of that.

Amazon has not only used technology as their differentiator/equalizer, they've also innovated in other areas of technology and now resell that to others. Amazon is definitely a tech company on that measure. Zappos - they sell shoes. Now maybe they've done some innovating/inventing themselves, but I don't think they are known for that aspect of their company.

Not sure if you're aware, but Zappos is owned by Amazon.

Guessing he or she means they sell shoes, not software or hardware.