Is it true

I understand the government are giving consideration to allow tourists to return possibly around October 2021 with no restrictions providing a tourist can present a valid up to date certificate issued by the country of origin that you have received the necessary vaccinations against the COVID-19 virus.

Sorry to disappoint you but it's not true.

Cambodia will closely monitor the "sandbox" initiative of Thailand's Phuket, where vaccinated travelers don't need to go in quarantine.
If it works it's fine and there might be a reaction from Cambodia but don't expect anything before the end of the year.
Mandatory stay is 2 weeks, after that people can travel freely to other parts of Thailand.
If there will be a cluster of infections  in Phuket it's back to zero.
The sandbox initiative starts this month.

Cheers.

Joe