Quite simple. The devil does not create man. Therefore, the devil does not and cannot give "characteristics" as a temptation. Biology (God?), however, does indeed render characteristics. And there is plenty of studies that suggest a genetic/epigenetic determinant for homosexuality. One study demonstrated that when one twin is homosexual, the other twin would be homosexual in 66% of cases in identical twin pairs and 30% of cases in non-identical twin pairs (this includes twins raised in separate families). To put this into perspective, the likelihood of two random people both being gay is likely much less than 1%.

If you want to know more about epigenetics, please ask or look it up. Suffice it to say, it means that our genes very strongly influence our traits but other things (e.g., prenatal hormone exposure, the environment, etc.) may affect how those genes are expressed. This explains why a grossly disproportionate number - but not 100% - of twins share a sexual orientation.