I would look to see what stage you're at as a start.

I've ben through this many times.

1. First study the VC and the partner
2. See what else he has invested in
3. They may be looking to round up their vertical with something similar or to acquire smaller players. If you're not a competitor, then anything is game.
4. Study when they invest and how

Lastly:

1. Set up the call.
2. Start the call by letting them talk a lot first. Ask: What is your mandate, sector? What do you invest in? What stage? What do you look for? What is the typical investment size? Where (geographically) do you invest?

This will tell you a lot about why they are reaching out and what you should say after.

Hit me up privately if you would like to discuss more, and good luck!!!