Is this 30 minutes walk billable to us?
This is something you'll need to ask the international IT company, as it depends solely on your agreement with them. It's not a lot different from the question "is lunch break time billable?"
Personally, if I had a team of contractors working on a project, and I saw them all taking 30-minute walkaround breaks every day, I'd be very concerned. I would go back to the contracting company and ask what was going on. And my contract with them would typically allow me to have any or all replaced if they weren't working up to my expectations.
If I thought the 30-minute break was necessary (it usually isn't), and the working being produced was better for it, then I wouldn't complain. And a one-time or very occasional 30-minute break when stuck is perfectly reasonable.
But anyone who gets stuck repeatedly and needs to take 30 minutes to get unstuck is demonstrating that they aren't sufficiently qualified to work at a client site. I'd have them removed and replaced with someone who didn't get stuck so often.
TL;DR: When you want to know what is billable and what is not, read your contract and talk with the contracting company. That's the only way you will know for sure.
Please note we are not asking if it is billable in a specific case, but to understand how it usually works since we have never worked with an outside consultant programmer.
"How it usually works" isn't as important as how you want it to work. Get it included in the contract, and whoever accepts the contract will do things the way you want without regard to how others do it.