You are essentially correct under normal circumstances. However, only the first six months of Sick Pay are subject to FICA withholding.
However, an Executive Order signed by former President Trump did this:
Starting with pay dates on or after September 1, 2020 the 6.2% employee portion of Social Security tax can be deferred for employees making up to $4,000 in applicable wages on a bi-weekly frequency, not to exceed an annual pay of $104,000. The repayment of the deferral is due December 31, 2021.
Please check with the insurer to see if this is what it did. (reference IRS Notice 2020-65)
