By my understanding, the case for stimulus checks leading to inflation comes when the stimulus checks are paid for by printing more money (thus increasing the overall money supply).
This program is not that. This program is providing a tax refund from CA's tax surplus. No new money is being created. The only change is who gets to decide how the money is being spent? (e.g., the state? or the people?)
If CA could have seen the future, they could have achieved the same end by lowering taxes this last year for people in an equivalent amount. Would anyone seriously argue that lowering taxes is inflationary? How about the contrapositive? Would anyone seriously argue that we should fight inflation by _raising taxes_?