Not necessarily, and it is worth understanding what that facility actually is before drawing conclusions about what the placement means.
The Substance Abuse Treatment Facility and State Prison at Corcoran, known as SATF-CSP, is a California state prison specifically designed to house male inmates with substance abuse histories. It is a full state prison that houses inmates across various points in their sentences, not a pre-release facility or a transitional program. Being designated there means the California Department of Corrections and Rehabilitation identified substance abuse treatment as a priority need based on his history and classification assessment. It does not mean he is close to the door.
That said, being at SATF is not a bad development. The programming available there is more focused and more intensive than at a general population facility. Inmates who engage genuinely with the substance abuse treatment programming at SATF are building a record that serves them well when they do go before a parole board or reach their release date. Completion of treatment programs is one of the factors that parole boards weight positively when evaluating whether someone is ready for supervised release.
The release timeline is still governed by the sentence itself, whatever good time credits apply, and any parole eligibility built into the commitment. His case manager at SATF can give the most accurate picture of where he stands on his release calculation.
Encourage him to engage fully with the programming while he is there. It is the highest-return use of his time at that facility and positions him better for everything that comes after.