They had some more details in yesterday's Khaosod news.
The car driver, 36 year-old Setawud Phadeeun, confessed to the incident and said he will pay for all damages. As I understood it from the article, Setawud claimed it was sparked by the 49 year-old Grab driver getting in his way and cutting him up with her vehicle. He was also stressed about his electrical sales business and was just on the way to collect 30K Baht owed to him from a client.
At one point the Grab driver started rebuking him, causing him to lose it, get out the car and hit her on the head with his gun before fleeing the scene. He claimed it was an air gun (BB gun).
Setawud said he initially didn't realise it was a woman and thought it was a man.
She required 12 stitches for her head injury.
There's a small clip of him at the police station (shirt on this time), where for some reason he bought along his baby daughter.