I will try to respond without having even a 3rd rate thinking ability. I did not copy and paste this response from a website. I did my own research.
You are close, but not quite right. From an originalist perspective the commerce clause is not what allows a state to quarantine people, police power is.
They form a portion of that immense mass of legislation, which embraces every thing within the territory of a State, not surrendered to the general government: all which can be most advantageously exercised by the States themselves. Inspection laws, quarantine laws, health laws of every description, as well as laws for regulating the internal commerce of a State, and those which respect turnpike roads, ferries, &c., are component parts of this mass.
No direct general power over these objects is granted to Congress; and, consequently, they remain subject to State legislation. Gibbons v. Ogden, 22 US 1 - Supreme Court 1824
In giving the commercial power to Congress the States did not part with that power of self-preservation which must be inherent in every organized community. They may guard against the introduction of any thing which may corrupt the morals, or endanger the health or lives of their citizens. Quarantine or health laws have been passed by the States, and regulations of police for their protection and welfare. Smith v. Turner, 48 US 283 - Supreme Court 1849
The right to so seize [poisoned food] is based upon the right and duty of the State to protect and guard, as far as possible, the lives and health of its inhabitants North American Cold Storage Co. v. Chicago, 211 US 306 - Supreme Court 1908
I hope my defective thinking as you explained it did not impact my reply to negatively.