The estimated difficulty was to be around 1.59M and we ended up with 1.56M
It is hard to say for sure how much these attacks effected the retarget, but i think they did somewhat.
That's just ~1.886% change and it may be caused by another factors.
I can estimate that you would have to block all pools and solo miners for more than 6 hours completely to make a 2% change
if the hashrate is not growing.