It doesn't mean that he's a sensor, but it means he enjoys using Se a lot. If he were ENFP, Se would be expected to be dead last in his order (not that that's something I've ever observed in real life ENFPs; in fact, they tend to be very Ne/Se balanced in my experience).
Of course, if he's ESFP, he uses a lot of Ne, so the point is moot.
One thing that's interesting about Luffy is that he can probably be best described as always seeing things in terms of possibilities (Ne), but possibilities for experience (Se). So he might be a bit of a hybrid, using those two processes together in an idiosyncratic way.
Well, at any rate, I'm happy to concede that I'm not sure
he's a sensor.