I think I found an answer to my own question. I'm not sure how much weight a memo of legislative intent by the original author of California's knife law has on a DA's decisions on whether to prosecute, but I found a clarifying document at this page.

The relevant section of the memo discusses what types of knives are exempt from the category of a switchblade:

Quote:
...In order to ensure that only legitimate one-handed opening knives are covered, SB 274 narrows the language to only allow knives to fall under the exemption from the switchblade law if that one-handed opening knife contains a detent or similar mechanism. Such mechanisms ensure there is a measure of resistance (no matter how slight) that prevents the knife from being easily opened with a flick of the wrist. Moreover, a detent or other mechanism is prudent and a matter of public safety as it will ensure that a blade will not inadvertently come open.

Although some one-handed opening knives can be opened with a strong flick of the wrist, so long as they contact a detent or similar mechanism that provides some resistance to opening the knife, then the exemption is triggered...
(Emphasis mine)