Does the 800k baht deposit for a retirement visa need to originate from the same country as my passport?

The deposit for a retirement visa in Thailand does not need to come from the same country as your passport. You can transfer funds from anywhere overseas, provided that the account is in your name and the money is transferred to your Thai account also in your name. Some immigration offices may require proof of foreign origin of the funds, but this is not universally applicable; for example, the Chiang Mai office currently does not require this proof.