Blue Cheetah Analog Design interview questions

They had just 1 round of interview going over resume. They made a verbal offer and asked for payslips and documents which I gave. They mentioned they wanted to talk to my current manager and references . I did provide references, and they spoke to my reference. I was on immigration and no way I could let my current company or managers know I will be appearing for any interview. Also it's highly unethical to base any recruitment based on current manager no matter how casual it maybe. How can any manager appear for his subordinate interview at a different company. They never replies thereafter