You were misinformed. California will tax that income.
If all your work is actually (physically) performed in your state of residency and you never physically work in any other state, then you would have NO "other state income. "Currently, the only exception to that is California. Due to a 2019 court ruling in CA, if you are a sole proprietor and you provide services to a client located in CA, that income is taxable by CA - even if you never set foot in California.
