Pass youtube-dl the -F parameter to see all the video formats available. In this case:

    [info] Available formats for 0_gaag5ixq:
    format code  extension  resolution note
    hls-meta     mp4        multiple   Quality selection URL 
    mp4-467      mp4        640x360     467k , isom container, avc1, 29fps, ~9.29MiB
    hls-478      mp4        640x360     478k 
    mp4-664      mp4        640x360     664k , isom container, avc1, 29fps, ~13.10MiB
    hls-679      mp4        640x360     679k 
    mp4-904      mp4        640x360     904k , isom container, avc1, 29fps, ~18.00MiB
    hls-925      mp4        640x360     925k 
    webm-1436    webm       1280x720   1436k , webm container, v_vp8, 29fps, ~28.50MiB
    mp4-1453     mp4        1280x720   1453k , isom container, avc1, 29fps, ~28.90MiB
    hls-1487     mp4        1280x720   1487k 
    mp4-2455     mp4        1280x720   2455k , isom container, avc1, 29fps, ~48.80MiB
    mp4-3884     mp4        1920x1080  3884k , isom container, avc1, 29fps, ~77.20MiB
    mpeg-32358   mpeg       1920x1080  32358k , mpeg-ps container, mpeg video, 29fps, ~627.00MiB (best)

So, you're both right.