Is it possible? Yes. Once the visa is issued it doesn't matter where you fly to Thailand from.
But there have been reports of people being asked for follow-up documentation proving they are either in the country or still in the country if the embassy gets any hint that you left. If that happened to you and they found out you left already, they would cancel your application.
so it's definitely a scam. One of the most popular for a long time. After he pays for the medical certificate then there will be another problem that needs 2000 baht. Then after that another problem for 1000. On and on
as I mentioned, no one should ever extend an OA visa. What most people do with an OA visa is buy it from their embassy and then go to Thailand. Right before the expiration date of the visa (the date on the visa from the embassy, not the date on your entry stamp) they leave and re-enter Thailand after they purchase a new year of insurance. This gives them another year of permission to stay in Thailand, as if you remember I said each time you enter during the visa validity you get stamped in for a year. But during this second year your visa has already expired so you cannot get more time. So near the end of year 2 you take a trip back home. Visit some family, eat some comfort food, and apply for a new non-OA visa from the Thai embassy at home. Then return to Thailand and rinse and repeat every 2 years. This means you'll never have to show that you have money in a Thai bank account.
You applied for a motorcycle license online? What? A motorcycle license from Australia? From Thailand? Where are you at? You cannot get a Thai license online. You must go to the DLT office and apply there.
If someone is telling you that you can get a Thai license without going to the DLT then you've just fallen for a very common scam. And you're going to keep getting asked for money until you finally stop sending it.
How do you expect them to do a medical certificate for you when you're not even there? A medical certificate costs 100-200 baht at any clinic in Thailand.