There is no 30 day visa on arrival. Countries on the specified list can get a 14 day visa on arrival. I suspect that you got a 30 day visa exempt entry when you arrived.
Regardless of which airlines you use you would be in transit at BKK and would not need to go through Immigration. Even if you did, then they would give you a 30 day exempt stamp in your passport. No visa required. When you return in November you will get a 30 day exempt stamp. Check the "remain until date" on the stamp that they put in your passport. If you need to stay longer you can always get a 30 day extension to this date from Immigration for (I think) 1,900 thb or you can do a land border crossing and get a new 30 day exempt stamp.
I understand that Thai Immigration is putting this pressure on the Embassies of all countries. I would not be surprised to see the other embassies following the lead of the British. I believe that the Thais will pressure us all into making deposits into their banks as a way of staying in Thailand.
I believe that it is true that some agents and some Immigration people were arrested. Apparently agents were putting the money into applicants bank accounts. Then paying the bank to provide a false letter stating that the deposits had been in the accounts for the required time. Once they had the letter the agents then withdrew the funds from the applicant account within the same day. The Immigration staff were complicit in accepting the application without sufficient proof of the funds after they accepted money from the agents. No knowing how far the department will go with their crackdown. But the new boss is a relatively junior officer for that position. It is known that he is ruthless and wants to make his name to secure further promotion.
Not good. Thin edge of the wedge. Thai Immigration already want US nationals to prove their income. Now UK will no longer issue, they say, because they cannot confirm income figures. Australian Stat Des are still accepted. But for how long. Soon, I believe, only way to get a retirement / Marriage Visa will be to have the require funds in a Thai bank. Poor show for us expats.