Diana, Princess of Wales died on Sunday, 31 August 1997 following a car crash in Paris. There was widespread public mourning at the death of this popular figure, culminating with her funeral at Westminster Abbey on Saturday, 6 September 1997.
Princess Diana's funeral was within the same month as her death.
It is definitely incorrect because Princess Diana's funeral took place in September, as opposed to August. The AI probably got it wrong because it did not keep track of the name of the month in which her death and funeral occurred. 
( z1 funeral :poss ( z2 person :name ( z3 name :op "Princess" :op "Diana" ) ) :time ( z4 after :op ( z5 die :ARG1 z2 ) :quant ( z6 up-to :op ( z7 temporal-quantity :quant 1 :unit ( z8 month ) ) ) ) )