Why did I get charged with Assault 3 when the person only suffered bruises?

Assault 3 can arise from:

1. Recklessly causing serious physical injury to another person while using a deadly or dangerous weapon;
    
2. Recklessly causing serious physical injury to another under circumstances manifesting extreme indifference to the value of human life;
    
3. Recklessly causing physical injury to another by means of a deadly or dangerous weapon under circumstances manifesting extreme indifference to the value of human life;
    
4. Intentionally, knowingly or recklessly causing, by means other than a motor vehicle, physical injury to the operator of a public transit vehicle while the operator is in control of or operating the vehicle (Public transit vehicle means a vehicle that is used for public transportation or operated by or under contract to any public body in order to provide public transportation);
    
5. While being aided by another person actually present, intentionally or knowingly causing physical injury to another;
    
6. While committed to a youth correction facility, intentionally or knowingly causing physical injury to another knowing the other person is a staff member while the other person is acting int he course of official duty;
    
7. Intentionally, knowingly, or recklessly causing physical injury to an emergency service provider, while the emergency medical services provider is performing official duties;
8. Being at least 18 years old, intentionally or knowingly causing physical injury to a child 10 years old or younger; or
    
9. Intentionally, knowingly, or recklessly causing, by means other than a motor vehicle, physical injury to the operator of a taxi while the operator is in control of the taxi.

Bruising presumably would constitute physical injury (impairment of physical condition or substantial pain) and not serious physical injury (physical injury which creates a substantial risk of death or which causes serious and protracted disfigurement, protracted impairment of the function of any bodily organ).  Because causing physical injury, by itself, normally constitutes Assault 4, one of the above listed additional conditions would be necessary to make it Assault 3.