i havent seen too many 50kg fish in my life, but i reckon its a big call to look at a fish and speculate (judging by the story of this capture i dare say this fish was certified).
i see many tricky lense work photos, and this honest pick like this is the best gauge, IMHO, side by side... regardless of apparent fish stretching. dont forget the flesh density of sea creatures is probably less than land animals. i think get a scale out (using a sling) and back it up before you lay claims, be you a bass fisherman or a gt freak.
if we asked most fisherman all our p#nises are atleast 8inches long!
to add on to my rant, just think... how many of your girlfriends and wives weigh less than 50kg? if you dont have a 50KG to pick up try picking up two 20kg rice bags!
may i say also that is an awesome fish, a shame it died, and they cheated in using bait!