Not necessarily a lie, you would like to join them for drinks...just without alcohol in your particular drink. And yes I know "drinks" the way they said it assumes alcohol, but I also look at it as you wanted to let them know you were interested in getting together to get to know each other right? So that part was true. And having something to drink is just fine too. How about some fancy coffee drink and you can catch a caffeine buzz to help keep you in a talkative mood?
All you're removing from this entire equation is the alcohol part. And yes I know all of this is hard in the early days. So you have to realize your boundaries, and then you can expand them as you get more comfortable being around social settings involving drinking. If I don't want to have to explain why I don't drink I still occasionally just tell them that I have an allergic reaction to alcohol. It's not really a lie as I believe my body processes alcohol differently than a normal person. Symptoms include "foot in mouth" syndrome, hermititis, and on rare occasion breaking out in handcuffs.