No mechanical issues these days with cars. Either incompetent driving, or, more likely, mobile phone use when the light had already turned green and she hadn't moved.
In general, Thais might be able to move a car, but certainly not drive a car. The evidence is there to see every day, also look at how locals obtain driving licences. So maybe, just maybe, the Russian had a point. That does not excuse his conduct , though.
A 'little beep on the horn' is the worst suggestion you could make as it might really provoke a Thai driver. Honking is not appreciated in TH.