(...) Keypad_I2C library. That library adds support for using a matrix keypad with I2C port expanders
I think the library doesn't refer to any sort of "i2c keypad", but rather a way to build one by tying rows and columns pins of the keypad not directly to the arduino pins, but to a i2c port expander.
Searching for
arduino i2c port expander
brings up a lot of interesting links...
HTH