Michael Coe, 35, stopped driving and allegedly confronted the 16-year-olds, demanding to know if they were Muslims.
When they lied and told him they were not, he grabbed the boy around the neck before throwing him to the floor.
At Southwark Crown Court Mr Coe, a Muslim, denied assault occasioning actual bodily harm and battery.
He admitted assaulting the 16-year-old boy in Wilson Road, Newham, on 15 April but claims it was self-defence.
The boy, who cannot be named for legal reasons, told the court he was hugging his girlfriend goodbye when Mr Coe shouted "let that little schoolgirl go".
He said Mr Coe grabbed him by the throat, causing him to black out.
He said: "I woke up - there was blood on my hands and I could feel blood on my face, my head was throbbing and I was very dizzy and also felt sick."
The court heard schoolteacher Boutho Siwela went over to help the pair when Mr Coe also allegedly attacked him.
Prosecutor Jonathan Polnay told the jury: "This case is about what started as unpleasant bullying with religious overtones in the street, followed by an attack by this 35-year-old man on a 16-year-old schoolboy.
"This was completely unpleasant and utterly unwarranted - this is a grown man on a child."
A "bully" grabbed a schoolboy by the throat and called a teenage girl a "whore" after spotting them cuddling in east London, a court has heard.