2004 Chevy Impala Leak afte water pump rplacement

I had a local mechanic replace the water pump on my 2004 Impala 3.4 V6 (since it needed a thermostat anyway, and I didn't have the proper tools). Since the repair, I've noticed small puddles of what appears to be transmission fluid under the car. At first I thought it was oil, but though the consistency seemed right, the color didn't match. My question is - is there anything in replacing the water pump in these cars that, due to negligence, cause an oil or transmission leak?
Thanks!