That is standard practice for a lot of shops, We offered a free alignment check with every tire purchase (sometimes with every oil change or anytime), but a free check does not mean it is a free set, nor does it mean it is out… It is no different then a free brake check, doesn’t mean your brakes are bad, it is a numbers game… If you never ask a nice lady out on a date then your chances of getting a date is slim to non, if you ask a lot then you have a better chance of a date…
The reason Discount tire does free flat repairs is not because they are nice people, it is because half the flats are not repairable and they have a higher chance to sell a tire or more…
With todays alignment racks/machines it only takes a few minutes to check an alignment and if it is out then you have a much higher chance to sell the alignment then if you never checked it in the 1st place… Remember, just because a tire is worn and has bad treadwear doesn’t meant the alignment it out, it could be prior wear from before the alignment was set last week or not to long ago at a different shop… So a free check is a very good business decision…
BTW I have had vehicles towed in with a blow out from hitting a large pothole etc and the car needs all new tires and looking at the treadwear and the damaged tire from hitting something sell the tires and presale an alignment, just to get it up on the alignment rack and find the alignment was perfect, so I just changed the set over to a free check and the customer was very happy the bill was less…