The term "OES" (Original Equipment Supplier) is nothing new ... and an OES part is the same as an "OE" part - ie, a part supplied and used in the manufacturing of the vehicle on the factory assembly line (same as your first sentence). If the same exact "OE" part is also sold through the dealership as their branded part (ie, Toyota, Ford/Motorcraft, Mazda, Subaru, etc), then it's now technically an "OEM" part.
Even if that dealership OEM part is made by someone different from who made the OE factory part (which happens quite often), then it's still an OEM part because it's approved, identified and labeled as Toyota, Motorcraft, Mazda, Subaru, etc. If someone else like Walmart or O'Reilly Auto Parts sells genuine Toyota or Motorcraft filters labeled as such, then those are still OEM filters. OEM parts can be the same exact part made by the same place as the OE part, but OEM parts can also be the same equivalent part made by someone else to the auto maker's specs, and it will have the same auto maker P/N and brand labeling. What it boils down to is that once any part is branded and sold as a genuine Toyota, Ford, Subaru, Mazda, etc branded part, then it becomes an OEM part.
A search for OES parts shows it's nothing new as far as terminology in the parts industry.