The obvious, here, is that you're friend is exceedingly comfortable with you. He TRUSTS you, Completely!
Does he want "more"? He is the only one that holds the answer. "More" just might be past his personal limits ... then, again ... maybe not.
Personally, I wouldn't "push" for that. But, like others have said, explore that possibility in Very Small steps.
In spite of what most of us, in the U.S. of A., are taught to believe, nudity does not equal sex! Some of us (though I was not one of them) are lucky enough to be raised with a view toward nudity as nothing more than it being perfectly natural. (Which, of course, it is!) Your friend just might be one of those lucky few!
The fact that he "popped a boner" means nothing more than his body was responding to physical pleasure. You must be quite good with your massage technique! But, you must keep in mind that ALL Guys, in your age range, often "get wood" for no Apparent reason! Heck! Just thinking about Thinking About getting Hard used to do it for me!
To find a Guy, who is so relaxed with you, that he lets you "simply play" with his body, with no other intentions, is pretty rare. You may never run across another quite like him!
Does it mean he is Gay or Bi? Not necessarily! Nor does his sexual preference really have to "mean" anything, here. All that you have discovered about him is that he feels secure in Your hands.
Keep in mind that the sexual "ideas" are coming from within You! There may be none of "those" intentions coming from Him!
By all means, Enjoy this! It certainly seems that Both of you are! And, there is a high possibility that you will get more chances to do this with/to him again.
However, above all, Respect his Trust in you! That, in and/of itself, is far more precious than any "happy ending" might be.
Of course ... no matter what ...
Keep smilin'!!


Chaz
