His answers became dry and short. What changed?

A shorter reply gives you less material, but length does not reveal warmth by itself. An answer to a practical question may be brief and complete; a one-word response to something important may leave the important part untouched.

The useful comparison is what changed in the exchange, not how to make your reply equally cold. If a question keeps going unanswered or the tone feels different to you, that specific change can be the opening.