There are two ways of stating an I2C address: with or without the R/W bit. The former is 8 bit, the latter is 7 bit long. You need to look up the data sheets of both the I2C device you are using, and the I2C library, which format they want to use.
In the code above, slaveAddress is a 7-bit-address, whereas the library / MCU wants a 8-bit-adress, so the address is moved one bit to the left.
Since the (UDB) I2C master in the PSoC want to use a 7-bit-address, you don't need the bitshift.