Why did my cat do this?

This blackish and grayish striped cat came to my front screen door today and looked at my tuxedo cat. They put their ears slightly back and their hair was pointed upright on their backs.. they would continue to howl softly at each other. Sometimes they'd get closer to each other and sometimes pull away. My cat had his tail down and looked uncomfortable while the other one looked normal.. the stray cat had a tag on so it must be someone's around the area. My mother needed to go out and so she attempted to nudge my cat out of the way but it softly hissed at her. this is the first time we've seen our cat behave this way in the two and a half years we have had him. He was a baby when we rescued him. So does anyone know why they acted this way? was it because of rivalry?