If you call a guy buddy and he calls you sweetie. Is this a good sign?

Depends on the guy I guess, I only use terms of endearment like that on the young and feeble. So for example a child whose name you don't know, "how can I help you sweetheart?" But other guys might be different.

If it happened to me, then Houston, we have a problem!
If it happened to you maybe....

Not at all a bad sign anyway.