I lived in Oregon for 21 weeks in the middle of 2022 and earned income remotely through my DC-based employer. Is that non-Oregon source income taxable by Oregon?

If you lived in Oregon temporarily, you must determine if you established DOMICILE. which requires you to file the resident tax return.  The rules for Oregon state:

You're a full-year resident if all of the following are true:

• You think of Oregon as your permanent home.
• Oregon is the center of your financial, social, and family life.
• Oregon is the place you plan on coming back to when you're away.

You're also considered to be an Oregon resident if you maintain an Oregon residence and spend more than 200 days in the state during the tax year. 

You're still a full-year resident if you temporarily move out of Oregon, and then move back.  You're a part-year resident if you stop being a resident of another state and become a resident of Oregon, or if you stop being an Oregon resident and become a resident of another state, during the tax year. 

If you established your Oregon residency, the income you earned working in Oregon while you lived there is Oregon-source income.