The scientist gags Lois before placing her on the platform above the molten metal, even though he's trying to intimidate her into revealing the location of the missing jewelry. Even if she wanted to, she'd find it impossible to tell him.
After robot #13 has robbed the House of Gems and flown off with Lois Lane in its hold, Superman flies up and attempts to rescue her, causing an "Interference" alarm to sound. It is not explained why this alarm did not sound when Lois climbed inside in the first place.
When Superman "Interferes" with the flying robot, the mad scientist presses a button which causes the robot to jettison the cargo. Therefore, he should not seem so surprised when it arrives empty-handed and demand of Lois Lane what she's done with the gems.