If your college degree was described in your resume and was a differentiable factor in your hiring they may have been forced to confirm it's accuracy or be open

If your college degree was described in your resume and was a differentiable factor in your hiring they may have been forced to confirm it's accuracy or be open to fair hiring lawsuits - for instance if you are white and another candidate black with him having a 2 year degree against your 4 year degree and all other things equal - if you lied about your 4 year degree then the black candidate would be more qualified for the position and, if preference absent any factual difference is given to white candidates often enough that can violate the equal employment opportunity act - if that happens often enough, the government can come down on the company hard. Additionally, a four year degree might qualify your employment for grant subsidies for research while a lack there of might make it harder for the company to justify - I've worked in a few places now where my employment has been government subsidized since I've worked on novel research. Basically, HR is stupid complicated and I'm sorry the experience was negative, but they were probably compelled to make sure they got that information to insulate the company from various legal exposures.