What are the current visa regulations for U.S. citizens entering Thailand?

Yes, it's the same for UK. You get 30 visa exempt but if you want to stay longer then apply for a visa in your home country. Here it is £30 with proof of income via bank statement, insurance and enough money to spend in Thailand. I think it is 40, 000 baht

You are confused about Thailand's different entry schemes. USA passport holders qualify to enter via either a 30 day visa exempt entry (no need for a visa) by just showing up, or with a 60 day tourist visa granted in advance from a Thai consulate outside Thailand. If residing within the USA, the tourist visa can be applied for online via Thailand's e-visa website. Either the 30 day visa exempt entry or the 60 day tourist visa can be extended one time at immigration offices within Thailand for 30 additional days. Americans don't qualify for a separate entry scheme called visa on arrival, which some nationalities must use, where they pay for a visa when they get to Thailand, which grants only a 15 day stay.

If you purchase a tourist visa before entering it is 60 days and can be extended an additional 30 days locally.

If you enter without visa it is 30 days and can extend another 30 days locally.

The image is correct.

If your son got 30 days they he didn’t have a visa (or the officer stamping him in didn’t see it). He entered on a visa exempt 30 day stamp.