NO....that question in the TTX software 1099-DIV form Q&A actually refers to any US bond interest that fund might report for $$ the fund distributed into for box 1a on the 1099-DIV form. From what I've seen of their holdings, that might be zero, or at least very-very small.
To find out for sure what % of the distribution is form US obligations, you need to get that information from some kind of supplemental sheet that American Century publishes (somewhere...call them and ask where to find it).
That same sheet of Info should also show what % of the portion of the $$ from that particular fund, that went into box 11 , came from CA bonds, and any US territories (I see they hold some Guam bonds)
On the follow-up page that asks the state(s) source of box 11, and "IF" you are a CA resident, you would break up $1000 something like this:
Multiple states.......... 5
"Multiple states" refers to the total of anything not CA, or not a US Territory (Guam, Puerto Rico etc) but may not be needed at all if the Fund did not invest in anything else.
Now, if you hold any other mutual bond funds, those $$ may be tossed into box 11 too, so you'd have to calculate each total together and add them up for the breakout....thing is, CA does not allow a breakout of the CA- portion unless the Fund owns 50% of it's assets in CA-only bonds. Certainly the American Century fund you specified here qualifies, but if you own other bond funds, they may not qualify.
And, as I indicated, you'll need to calculate the exact amounts yourself from whatever % breakdown each fund provides.