I thought the same shit when I saw your performance on this exercise, Dave.
I was like, 'WTF!?!?', but if that shit and form works for you then go on with yo bad self. 
look. i have modified my form on most movements over the years to suit me. i go by feel and how damned sore i get in the target muscle the next 2 days. plain and simple.
look at that still shot for a moment, please. isnt that the same exact anatomical position as a seated row? arent seated rows for back?? yes!
so, lets not call what i am doing "pulldowns", cause theyre not! theyre clearly not pulldowns. lets call them "ROW-DOWNS" ..they are "dave row-downs"
now...look again at that still shot, and you will see i am doing perfect "textbook form on ROW-DOWNS!!
I HOPE THIS MAKES EVERYONE HAPPY.