Do you think this was on purpose? Or just a botched update?

The access was intentional. The botch was presumably an error, but that doesn't matter. What matters is the "authorization" issue. Was HP authorized to access the computer? Probably. Were they authorized to damage the computer? No. There's room for legal argument.

CFAA: intentionally accesses a protected computer without authorization, and as a result of such conduct, causes damage and loss.

The point is that fighting this is a lose-lose for HP. Either HP has to argue in court that they have a contractual right to brick your computer, or they have to make you happy enough to drop the case. Visualize the press coverage of HP arguing on the record that they have the right to brick your computer.

Where are you getting "HP accessed the computer"? This was a BIOS update initiated by the end user.

It was rolled out through Windows update, so I'm not confident the end users authorized it.

Do you think "but it was an accident" should be an accepted legal route to escape liability for your actions?

Yes - the CFAA as a criminal issue requires "mens rea", the intention to commit a crime. Very few laws (such as involuntary manslaughter) have exceptions to this.

If you break someone's shit by accident, they can still sue you, and people should probably sue HP, but you can't try to have a prosecutor bring them to a criminal trial under the CFAA.

No, but it usually makes it civil liability and not criminal liability. For the most part (there are exceptions), you can't accidentally commit a crime.

For the CFAA? Absolutely.