Yes all the above observations are true.
I will tell you about some more traits about Indians and their nodding gestures...
1. Verticle nodding up down is Yes.
2. Horizontal nodding around the neck means No.
3. circular from shoulder to ear and other ear to shoulder means Yes
4. Strictly Horizontal (no round or circular motions) means a dancing \ enjoyment \celebration gesture. Its the typical indian classical dance i.e. BharatNatyam based gesture.