I’m inclined to lean toward this being a different individual. Gray Flycatcher is a regular spring migrant in the Central Valley and adjacent foothills and occasionally is found in abnormally high numbers along the coast and coast range valleys. This has been one of those unusual springs with multiple birds found at various locations from Humboldt County to Monterey that fits previous patterns. The best spring that I can recall was in the mid 1980s when about 16 were found in Humboldt County alone! My best migrant wave experience was in the foothills near Fresno where three of us found 45 in about two hours within a fairly limited area (~200 acres).
If this was a species as rare as Little Stint in the region, then I’d be more inclined to support the singe individual idea.
I'm inclined to think it is the same individual last seen at Ulistac Nature Area in Santa Clara, for a similar situation has developed with the Little Stint. With many birders on the lookout these days, it appears 'our' Little Stint has been spotted in Oregon. http://digest.sialia.com/?rm=message;id=1186400