Which lounge you went? There are two in the international departures. One at lower ground level nearby to gate and other one is level 3. Both are travel club lounge.
They will tell third floor lounge for business class only. But they will allow with priority pass or DCB or Amex etc till 7.30 PM. They don't encourage Rupay and debit cards. After 7.30 PM, they allow only business class and will push all others to lower floor one.