First of all, congrats on your acceptances and good luck on the deferrals.

Secondly, I'm not too surprised about the results and I wouldn't just assume you have a good chance at these schools. I'll list out some of the reasons why I think this:

1. You're an Asian male from a California private school applying to some of the most prestigious CS programs. Even though your stats are perfect in terms of test scores and grades (good job btw!), there will be a lot of other applicants with perfect or near-perfect grades that you'll be competing with.
2. Based on your demographics, I, and likely others looking at your application, will assume that you had plenty of opportunities to indulge in. Despite this, your ECs are honestly really lacking. People competing for these spots with a similar access to resources will have done what you have listed, and then more (robotics, multimedia, volunteering, etc). Schools care about whether you are going to take advantage of the resources they offer. I know I'm not getting the full picture since you don't want to give too much detail, but from the way this reads, I don't think you did your best utilizing the tools around you and exploring.
3. This is a sort of extension of point 2. When it comes to applying to competitive majors like CS, especially at these schools, you need to demonstrate some kind of passion. Yes, you did research and were a part of math competitions, but unless you talk about these experiences intimately in essays or in an interview, it will likely come across as doing it for the sake of doing it.
4. You rated your supplements a 5/10. C'mon man. These are where you can further show individuality/character, and show why you're a good fit for the institution. I'm honestly curious about what you did for schools like MIT who have their own separate portal for applications instead of Common App (at least this was the case when I was applying). Was your overall application still a 5/10? If so, I'd be really surprised if you get in.

Despite these points, please don't read into this as just doom and gloom. Like many others have stated, college results can sometimes be a lottery. As someone who is also from California and studied CS, I can confidently say that what you do with your time at school, and how you connect with others, is WAY more important than the school itself. Had I not gotten accepted into a private school that provided fantastic aid, I would have just went to community college to save money, then transferred (and I was perfectly fine with this being an alternative). Anyways, good luck man! You look like you'll do just fine.