I was fired after two days at my new job with no explanations. Is this wrongful termination?

Weight isn't a protected category under general principles of employment discrimination. In other words, an at-will employee can be fired for being fat.

Even if it were a protected category, they hired you. Assuming they interviewed you, they knew your weight when they hired you. So how could you prove they fired you on account of a condition that they knew about two days before?

At-will employees can be fired for any reason or no reason at all (except unlawful discrimination). You state no facts that make me suspect wrongful termination here.

Not legal advice as I don't hold California licensure. If you need legal advice, please consult a lawyer who does.

Good luck.

I agree with my colleague. You were an "at will" employee, and your employer changed their mind about you, or you did something you weren't aware of. Regardless, without a contract or a union to protect your job, and without iunlawful discrimination because of your age, race, religion, gender, national origin, etc., or some "wrongful termination" because e.g., you were a "whistle blower," your employer can fire you at any time without notice for no reason at all at their whim.

Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.