Incredibly, both drivers were cleared by the medical centre soon after, and competed during the second race in Iowa on Saturday.
Speaking to NBCSN pit reporter Kelli Stavast, Herta explained he did not realise IndyCar had called off the restart, prompting the collision.
"It happened so fast, I wasn't really sure what was going on, but I'm happy to report, I'm fine," Herta said.
"No injuries. I feel perfectly fine and fit to drive (in Saturday's race).
"I wasn't told the restart was called off … I was told green. I wasn't going to go by the lights when I was told green. So that's what happened. And there you go. I guess everyone else got the message. Happy to be okay."
The 20-year-old shared a video to social media thanking his followers for their supportive messages.
"Just got back from the medical centre and just got back here to the motorhome," Herta said.
"Just wanted to say thank you for all the kind messages.
"I'm 100 per cent okay, really excited to get back on track tomorrow. I've got some unfinished business.
"Unfortunately, what happened happened. I'm happy to move past it. I'm happy Rinus is OK, and can't wait for tomorrow."
Meanwhile, VeeKay told NBC Sports he was thankful for the sport's safety measures which potentially saved him from serious injury.
"I'm very happy, especially with the safety … The aeroscreen, it was destroyed," VeeKay said.
"Thank you to IndyCar for the great safety cell and let's go for it tomorrow."
