According to M-476, if you were out of the country for more than six months (but less than a year), you should provide documentation that you maintained ties to the US such as evidence of maintaining a domicile (home) like a rent or mortgage payment receipts and pay stubs, plus tax return transcripts. Here's the actual text:
If you have taken any trip outside the United States that lasted six
months or more since becoming a Lawful Permanent Resident, send
evidence that you (and your family) continued to live, work and/or
keep ties in the United States, such as:
- An IRS tax return "transcript" or an IRS-certified tax return listing tax information for the last 5 years (or for the last 3 years if you are applying on the basis of marriage to a U.S. citizen)
- Rent or mortgage payments and pay stubs
If you did have that evidence but didn't send it with your application, I don't know whether or not you can appeal the decision with "new" information.