Generally, it is not unusual for a young teen to be curious about their sexuality and to actively seek out sexually explicit material of both genders. Kids that age are easily aroused by all nudity. Their bodies are changing and hormones rage, especially in boys. My rule of thumb is that looking is generally out of curiosity. Touching, both with opposite and same sex partners, may also be normal curiosity as long as both are willing partners and near the same age.
Many people have same-sex encounters as young teens.
This is not usually an indication of sexual orientation at this age, just exploration. Boys particularly are interested in seeing if their sex organs are normal looking, if they are developing as quickly as others and often compare their penis size with every penis they can find. This may go on indefinitely. Make yourself available for questions, but be careful not to make reference to same sex issues, as this may cause him to question his own behavior and sexuality more than he probably is already. You want to make him comfortable talking about sexual issues without being embarrassed.