Yes, but the comment was about IQ, not absolute intelligence. The median intelligence is, by definition, 100 IQ, so the median IQ cannot be decreasing

There's always a lag, you calibrate the test based on previous results, not future ones. If intelligence is decreasing I'd expect every IQ test to keep scoring a median lower than 100 unless taken immediately after calibration. Once it stops decreasing they'd converge again.

The median IQ of successive generations may absolutely be falling