You may have misheard. You likely got towed for parking for more than 72 hours. This is pretty standard in cities throughout the US, and is certainly the case in Oakland. It's quite common to call "parking for more than 72 hours" something like "abandonment" ... how are they to know that you're just in the hospital?
But here's the thing: they almost never do this on their own (unless you're parked illegally in some other way). One of your neighbors probably called and complained: "there's an abandoned car in front of my house!" ... OPD will come and chalk it; 72 hours later, you get towed.
Fight the real power: find out which of your neighbors hates you :-)
/jordan