Best practices are not 9.7 gigs of data, designs, and calculations.
Edit: I am assuming that the 9.7 gigs was data, designs and calculations. Could have been the best cat pictures ever. I just don't know.
You are expected to distinguish between public-domain knowledge and company-confidential information. Public-domain knowledge includes knowledge that you can (legally) obtain without being a part of the company, that you had from before you joined the company (without being under an NDA), that the company chooses to disclose to the public itself like by publishing papers, etc.
At a new company, you can as such freely describe published patents (i.e., those accessible publicly, whether approved yet or not) from the previous company, however, you or your new company are not expected to be violating any approved patents. It generally helps to not even disclose those inventions at the new company.
"Best practices" are generally not confidential information belonging to a company, though that could theoretically be if they involve patentable inventions or trade secrets. Likewise, you are not expected to be taking out any documents on these best practices subject to copyrights.
However, in the more general case, it probably depends in part on what sort of agreements you've signed. It's also one of the reasons why non-competes do exist and are enforced in many places. As you suggest, if you're a project lead for $FOO technology at Company A and you jump to Company B which wants to get in the $FOO business, the reality is that you're being hired only because you're familiar with what Company A is doing and has learned about $FOO.
You may not hold a meeting and do a brain dump of everything you know about what you learned while at Company A (which might well violate employment contracts and would generally be unethical) but you'll absolutely be transferring knowledge. Of course, this happens all the time at some level when people move between companies.
But California does have trade secrets that only exist in your mind. If you leave a company and immediately start a direct competitor you'll always be vulnerable to a trade secret allegation. You just have to judge whether they'll actually come after you.
I'd recommend documenting your development practices to show you are doing your own work. But for a small company, just getting sued is going to cost half a million in legal fees.
If you are an employee at a competitor, in would never write or say anything about how your old company did it. If you know how to do it well, that's arguably just a skill you have.
There is no clear answer.
Some of our goals are in conflict, and the answer is not always to come down on the side of one of these goals, but seek some compromise that tries to get the best of both worlds.
But this case seems much closer to a clear case of theft, rather than corporate legal overreach.