Cham
Thanks for clearing this up.
Based on what you said, seems like the speakers addressed everyone ( regardless of thier religion) as brothers and sisters .
That is commendable and you should be honorered.
The greeting Assalam O Alaikum means " May the peace and blessings . of God be with you" and that goes for everyone in the audience.
You were in a good gathering with all the speakers greeting you as sister.
unfortunately you wanted thenm to say CHRISTIAN sister or Hindu Sister or Sikh sister, I do not see a.need for that.
You are a sister in humanity and that's why they say Assalam O Alaikum brothers and sisters.
That's my take.