Should I consider myself a resident of another state if I didn't earn any taxable income, it's not my permanent residence, but I lived in another state for over 180 days?

It depends. If you consider yourself in the nonresident state as a visitor, and you had no taxable income during this temporary period, then there would be no reason to file in this nonresident state.  

• Taxable income includes wages, self employment, interest from savings, dividends, rents, royalties and more.

Your 'residence' is the place where you actually live, meaning the house, apartment, or dwelling you consider your primary home, as opposed to a temporary location; it is defined by your physical presence and intention to stay there for a significant period of time, although legal factors like voting registration, tax filings, and driver's license can also contribute to establishing residency in a particular location.  Domicile is the common term used to determine your actual residence and intent is most important.

File a return in the state of your residence and/or domicile.