I experienced this too (in zsh shell, on Mac). For me it was the shell trying to pre-process the command line including the square brackets, before passing it to the motpy examples python script, and the solution was to enclose the detect_labels argument in quotes.

e.g. (also selecting device as cpu, since no cuda GPU on my Mac):

python examples/detect_and_track_in_video.py \
            --video_path=./assets/video.mp4 \
            --detect_labels="['car','truck']" \
            --tracker_min_iou=0.15 \
            --device=cpu