And the OP specifically told CBP that they were going to leave in August. CBP granted the OP entry, in part, based on that statement, imo. USCIS has recently stated that there will be increased vetting of ALL Green Card applicants. What that means is not completely clear to me. This is a tricky one. There was one case I remember, a few years ago, where a spouse was admitted via a tourist visa. She was questioned by CBP, and she said she would not submit an I-485 to adjust status because she was just visiting her husband. She changed her mind later and filed one. Later, during the Adjustment of Status interview (which ALL applicants now have), USCIS denied her AOS due to misrepresentation. I never heard the final outcome.
You're right. It's not black and white anymore. It might be worth consulting a couple immigration attorneys. I just don't know what the risk is in this particular case. I think I would either stick with the K-1 or marry and start the spousal visa process.