Probably not, and the question of why someone would lie to stay in prison an extra month is worth sitting with before jumping to conclusions.
Release dates in California's system are not always fixed and can shift for several reasons. Good time credit adjustments, program completions, or administrative recalculations can move a date in either direction by days or weeks. The CDCR offender locator reflects a calculated date based on the current record, but that calculation can change as credits are applied or modified. It is entirely possible that his date moved slightly and he is working from more current information than the locator is showing, or that there is a discrepancy between what his case manager told him and what has been entered into the system.
It is also worth noting that locator databases do not always update in real time. There can be a lag between when a date changes internally and when it reflects on the public-facing search.
The more important question is what lying about a release date would actually accomplish. An extra month of incarceration is not a benefit. If anything, an inmate who wanted to mislead someone would typically push a release date earlier to generate more support, not later. The pattern of lying that matters in these relationships usually goes in the other direction.
If the discrepancy bothers you, ask him directly where the October 31 date comes from and whether he can ask his case manager to clarify. That conversation should produce a straightforward answer. If it does not, that would be more telling than the date difference itself.