This one is fading, but the general advice still holds: avoid handing things to people with your left hand. Some take it further to not eating with the left hand either but you can ignore that these days.
Historically considered unclean — the left hand was used for personal hygiene, and I’ll leave the rest to your imagination — it matters more in traditional settings and religious places than at a South Delhi restaurant.
If you’re left-handed, don’t worry. There are quite a few of you in Delhi too.