They were probably on a treaty visa, Like E2 (which i have, it's not just for business owners/investors, employees can get this too) or T2 (The NAFTA equivalent). These visas allow you to live and work in the US for a very long time (extendable indefinitely for 2 years a pop in my case), but they have no dual-intent attached to them. They are a dead-end and if you want to stay in the US you need to start from square one with an H1B/Marriage or convince your employer to start a standalone green card sponsorship, which costs like $50k and 2+ years of processing, where the only benefit to the employer is that you can now get a different job.
It's actually kind of a problem, there's a lot of people on these visas who've lived and worked here for 20+ years with no viable route to permanent residency.