It is one of the most common things a driver's insurer will say, because it shifts blame from the driver to the person on foot. But an assertion is not evidence. Drivers are required to keep a lookout and to yield the right of way, and whether you were truly impossible to see is a factual question — not a given.
California follows pure comparative fault, which means that even if you are found partly responsible, you can still recover, with your compensation reduced by your share of the blame. So even in a case where visibility is disputed, being assigned some fault does not end your claim — it affects the amount.
The way to answer the 'came out of nowhere' claim is with proof: the crash report, the crosswalk and signal evidence, witness accounts, the driver's speed, and any video. Building that record is a core part of representing an injured pedestrian.