Small dot represents distant traffic, there will be an arrow coming off the dot representing the course. When zoomed out this might look like a small triangle, but it's a dot with an arrow.
The Green triangle means the traffic is close enough to prompt an "informational" alert, red indicates it's close enough to pop a "warning".
The distances depend on your Collision Alerts Threshold. A "Moderate" setting during cruise the green triangle indicates within 3nm, red indicates within 1nm. Relaxed and Strict change the thresholds +/- 20% ish.
Thanks,
Walter