There are a lot more variables that go into it.
If Bob the builder buys a house 40k under value, invests 10k into it while living in it and reaping the tax advantages, rents out a room to collect rental income, and sells after 2 years netting 30k + monthly rental income... that house is most definitely an investment asset regardless of how much furniture was purchased to furnish it.
Rich Dad, poor dad philosophy is excellent but really only covers very generic scenarios.