Which state do you live in? Actually, it could depend on your county or even your city. Because leases are complicated.
A leased vehicle is the property of the leasing company, which makes it "business personal property," so the company has to pay property taxes on the car, the same way you pay property taxes on your house. That's typically built into the lease payment -- they have to pay the taxes, but they get the money from you. Some areas specifically exempt lease vehicles used solely for personal use. So, the company might have been collecting the taxes from you, but then found out they weren't owed because of where you live.
Another scenario, although less likely, would occur if you leased the car from a dealer in a different state. Some states collect sales tax on the full price of the car. The leasing company buys the whole car, but they make you pay the entire sales tax. Other states only collect sales tax based on the value of the lease. So, if they collected the full amount from you up front, they might have realized that it wasn't owed and sent the refund.
This is all part of why leasing is a terrible idea in Texas. You have to pay sales tax on the full price of the car up front, and you have to pay sales tax again if you purchase the car at the end of the lease. You also have to pay property tax on the car during the lease term. These taxes could easily double your payment.