All std free at 27days after protected receptive anal once? condom was intact, he didnt cum inside, hiv test negative at 27days, is it conclusive?

Not yet: Conclusive negative HIV testing is TWO negative tests 6 months apart, the last test being after the last exposure to HIV or at risk sexual behavior.

Almost, not quite: Very low risk for any STD after this single exposure. Highest risk (even this is very unlikely) is rectal gonorrhea or chlamydia; that requires rectal swab test, valid any time more after 4-5 days. Best HIV test is antigen-antibody (4th gen), which is almost conclusive (98-99%) at 27 days and 100% at 6 weeks or more.