SamMobile has reportedly spotted security updates for the Samsung Galaxy S6, which should bring its patch level up to January 2019. This is not hugely unusual, except for the fact that this phone is now nearly 4 years old. It joins a very short list of devices this age to still receive official software support from its OEM.
https://www.notebookcheck.net/Galaxy-S6-receives-yet-another-new-security-update-from-Samsung.407716.0.html
Not Oreo, but Nougat. And so far, the update is only available for very few countries.