The thread you referenced is for a PCF8574 i2c i/o expander chip.
You stated that you have a MCP23008 i2c i/o expander so that thread will not apply.
The LiquidCrystal_I2C interface class in fm's currently released library only supports
the PCF8574 chip so it will not work with your backpack.
I've seen 3 different MCP23008 based backpacks and none of them use the pin mapping
you entered into the constructor.
The LIquidTWI library that I've seen is for
the AdaFruit #292 board, but the pin mapping you supplied in your sketchis not for that board.
I'm curious which backpack you have.
Trial and error is not good practice.
And in the case of the MCP23008 it could damage the LCD or MCP23008 if the guesses are wrong.
This is a case were the tiny details really matter.
You need a library that supports the MCP23008
and then you must make sure that it is properly configured for your backpack so the library is setting
the output pins properly.
There is no standard for how to wire the output pins of a i2c i/o expander to a HD44780 LCD
and so boards from different vendors wire it up differently.
And that is why I said you must first make sure that the library supports the MCP23008 and
then you must make sure that it is properly configured for your backpack.
When installing different LCD libraries, you also need to very carefully follow
the instructions as often times you can't have multiple installed at a time.
I have a unreleased add-on for fm's library that supports the MCP23008 but in order to use
it you must know the pin wiring for your backpack. This isn't something to guess at because
the MCP23008 has strong source and sink capabilities and could potentially burn up an LCD
if the library was told the wrong wiring.
--- bill