Why does my puppy keep having these funny turns?

Ok, so I have an 11 month old male Yorkie. He is a clever little thing, sits at all the roads when crossing, will even give you high 5's! I take him out every-other day, where we meet up with a group of people and their dogs. (About 9 other dogs, He has no issues with this) He happily runs along with these other dogs, off the lead and will not bark or growl. When he is on the lead is when everything goes to pot. Walking past people he will bark and make a performance, he has got better at this as he don't do it to everyone. When he does this people think he is vicious, when he is the complete opposite! We have a strong bond, is he being protective? On odd occasions when he has barked at someone they have come over and stroked him and he licks them to death an wags his tail! Why is he making himself look like this little ankle biter?! Please, any help, or suggestions will be much appreciated, Thanks. :)