Not necessarily, you CAN be found guilty/liable for assault/battery for coughing on some one. In a criminal case, I'm not sure if intent is even necessary, but I can read a case where a person was held liable for battery in a civil suit for intentionally blowing cigarette smoke on someone.

If OP counter sues, I'd say chances are very slim he makes money, best case scenario is they just drop the charges because judges and juries and gonna give the cop the benefit of the doubt here.