It is possible that shop, like many shops, does not have the skill or maybe their equipment is out of spec. Similarly, At my oil / filter change last week, My tires are now ready to be replaced. They read 3/32 on all but the passenger rear which is at 2/32. I suspect that I must have driven over a pothole or maybe snipped a curb that knocked the alignment off on that corner. When they install my new tires, they will do an alignment and I will be sure to look at all 4 corners to see if that wheel is slightly more out of spec than the other 3.
BTW ... there are 4 tire shops near me and NONE of them have ever done the alignment properly. I only use my dealer now and they have never missed on the first try. yes, it's about $40 more expensive but worth it since it's $40 extra I spend maybe once per year or less.