it's because your kernel expects 7 bit addressing instead of 8 bit addressing.
In 8 bit addressing you will have the slave address(7bit) + read/write bit (1bit).

In 7 bit addressing you will right shift the bit once, so that read/write bit will be removed and you'll get only the slave address which is enough to detect the device present at that address.

Read more about 7 bit addressing in linux.