The chance of him winning the popular vote is high, but not as high as winning CA, which is a lock. It's greater than 99% that he wins California.
This is a weird election for many reasons. Turnout will likely be a lot higher. You'd think the turnout would favor Biden, but it's not certain. It's possible that this "silent majority" really exists, and they'll show up for Trump. It's much more likely Biden wins the popular vote, yes, but it's not the same as CA, where Biden is so far ahead that he basically can't lose.