No sign of mis-alignment on the outer edges?
Noting that the SA probably has some kind of up-selling target to hit and will therefore try it on with every customer, there is a faint possibility that they got the customer/car mixed up (so there's some other owner out there driving around on 'semi-slick' tires without realising it), and - rather than admit the mistake - kept right on digging...
Maybe use that as an approach for a question to the Service Manager?
