No misunderstanding or misquoting.I think you are misunderstanding or misquoting those figures
virus is projected to cost £645bn
Benifits from brexit referendum result to bring in £445bn
645 - 445 = 200
therefor the Virus will be no more damaging than the The 2009 financial crash that cost £200bn
QE (money printing) after the referendum result ALONE was £445bn
Nothing to do with the other figures.
Thus the referendum cost less than the virus ALONE is expected to do by the end of 2020, but over double the cost of the financial crash ALONE.
And at some point it all has to be paid back.
Simples