On it's face then, it is unconstitutional.
Yep, you are clear. What the Kansas 'Romeo & Juliet' statute did was reduce the sentencing standards for oral sex in cases where the younger teenager is 14 to 16, the older teenager is under 19, the age difference between them is less than four years and there are no third parties involved, the maximum penalty is 15 months in prison. The rule simply wasn't applied in cases where the partners are of the same sex.
BTW, the 18 year old in this case didn't receive oral sex, he provided oral sex, if you catch my meaning....