I'm not 100% sure but it doesnt sound aggressive barking to me. He didnt growl or anything.
It was the same type of barking like he would bark at the cats when he is on the lead and they move and we don't let him run towards them.

I just grabbed his lead in the town situation and walked away from the other dog pulling him behind me.

I wouldnt say he is aggressive towards other dogs as at the training he barked too but then calmed down and just watched the other dogs.