ffmpeg use of ildct flag in progressive encoding

I’ve encountered a scenario whereby someone else has configured an ffmpeg encoding command with flags that don’t make sense, and I’m having difficulty understanding their purpose.

The command in question is:

ffmpeg -loglevel info -y -r 29.97 -start_number 0 -i image_sequence_%4d.png -vcodec dnxhd -vf format=yuv422p10,colorspace=bt709:iall=bt601-6-625:fast=1 -b:v 220M -flags +ildct output.mov

I’ve been struggling to find information on what the addition of ildct does to the output in this case. It appears to be influencing the media to perceive it as interlaced, even though it is, in fact, progressive. Using the flag ildct seems counterintuitive and unproductive.