Why Did I Bleed After Having Pumped Breasts?

I pump exclusively and my right breast was very sore and hurt a lot yesterday. When I pumped last night, nothing but blood came out to begin with and immediately my breast felt better. I have had this happen a couple of times before but there seemed to be more blood this time around. When I looked at the milk in the bottle there were a couple of clots in the bottle. I have pumped 3 more times since then and haven't experienced it again. Could I have had a ruptured milk duct?