Yes. if he had just swung the bat then the time to find out if he also had a gun is before he pulls it out. Not after.
If he stayed in the car he was essentially locked into a space he couldn’t defend from a known weapon. Busting a side window out throws hundreds of tiny glass shards in your face and allows a bat or stick to then be drilled into your face lance style.
If he drove off he was vulnerable to a potential gunshot. By opening the door he was able to knock him off balance and neutralize both types of attack.