This poll shows significantly different results than most other CA polls over the last month. What has changed in that time? Cruz has had more big wins than Trump has. And do California Republicans really care what NY did?
Besides Wisconsin what other big wins did Cruz get?
Utah, Colorado, North Dakota, Wyoming.
What other big wins did he get where there was an actual election? Yes Utah counts.
Whether or not the media plays them up the same way or not doesn't diminish their significance. If you want to discount them for their delegate selection process, that's up to you. It's how those states GOP voters/parties pick their preference for President. And Cruz dominated them.
In terms of affecting "momentum," though, it does matter. It's actually plausible that the wins there gave Cruz a negative boost, as he comes across to some people, rightly or wrongly, as trying to steal the nomination undemocratically. I think Trump's bashing the process is working strongly in his favour. At the very least, it's working a lot better than basically calling Heidi Cruz ugly.