@citywolf It's not like racism. However I think I understand where she is coming from.
When you have a great dog that everyone judges based on its breed, I can understand how that could hurt. I love when I have my dogs out and people want to pet them because it makes my dogs very happy. Maybe her dog loves it, too, and it just makes her sad because people fear or hate the dog she loves so much.
It was ignorant of her to equate it to racism, and rude of her to lash out. She could have just as easily smiled warmly and said I know he looks scary, but he is very friendly and a gentle giant.
Conversely, you could have smiled and said it's not him (pointing to her dog), it's him (pointing to yours). Then maybe you would have had a nice but short chat from across the road and you both would have left feeling slightly better for the interaction.