Could be fear. This is a good time to introduce "enough" or some other 'hush' word. When we were out walking after dark at my mother in law's, Grim alerted on some noisy teens walking down the road. (He's always more on alert at night) I just told him "enough" and kept walking with him. He's not done that before, but we usually don't encounter people at night. We were also in a strange town, strange everything. BUT, he's getting older. I didn't see any hackles, but I want him to stop when I tell him to stop. He's never barked at friends or family members (even though he'd just met my MIL, he was great at her house and with her!) so I don't know what to tell you about that one.
This was during the day, though?? If so, maybe more socialization...
Wrath of Grim z Dragon
"Mr. Grim"- Threaten my handler. I dare you.