But the Pakistani population is growing. The Bangladeshi population is growing.

Pakistani was hit by a big flood that affected lots of people -- not merely because the flood was so big (it really was!), but because there are so many people in Pakistan that many of them have to live in risky places. Bangladesh is regularly hit by floods, which largely affect areas where people didn't use to live, simply because there are so many people in Bangladesh that many of them have to live in risky places.

Bangladesh is also flood prone due to misfortunes of geography (nothing at all to do with climate change or population explosion).

And then there are the local effects of large populations: felling of mangrove forests in Bangladesh, deforestation in general (Pakistan), people living on former meadows, people putting in barriers that prevent minor local "floods" (really just temporary widening of rivers) which lead to major floods, ...

And, yes, there is also climate change => deglaciation, more rainfall, and more extreme weather.

But anybody who tries to downplay the role of population growth in the recent disasters in Pakistan and Bangladesh is lying to you and probably trying to sell you something.