They haven't been beaten by 20 since Kap's first game, 5 games ago. They lost to the Cardinals by 3 a couple weeks ago. They kept within 13 of the Patriots.
They lost Gabbert's last 4 starts by 57 total points. They've lost Kap's last 4 starts by 51.
Going literally they've only lost by 20 or more just once this season to the Bills. They've lost 5 games by 15 or more, which is pretty much the definition of a blowout in my book.
Going backwards:
Pats 30 Niners 17 [-13]
Cards 23, Niners 20 [-3]
Saints 41, Niners 23 [-18]
Tampa Bay 34 Niners 17 [-17]
Bills 45, Niners 16 [-29]
Cards 33, Niners 21 [-12]
Dallas 24, Niners 17 [-7]
Seahawks 37, Niners 18 [-19]
Panthers 46, Niners 27 [-19]
Niners 28, Rams 00 [+28]
That's 5 blowout losses and I think in several of them the Niners got a score late after the issue was decided, so some of those losses weren't really that close.