I think this might be normal, I am a trans masc (still a bit dyphoric) but the same happens to me. Every time after a 30 min workout with my siblings, I go to the bathroom to take my shirt off for a bit, but then I feel like I've been turned on. No I am not from Alabama nor turned on by my own siblings. I just feel horny, idk why.
It's normal. The better shape you are in the more likely you are to have a higher libido.
Yeah. Possibly, it is due to the relase of endorphins which your workout caused. As crazywillie sez, amazing what the body does when you work out. After I go for my jog and take a shower, I get an erection sometimes. I can usually control it. But maybe it's from being in a strange place that you have a hard time controlling it. I find, with the penis, it's often a matter of reverse-psychology. When you don't want an erection, it comes up and stares you in the face, when you want one, you can't get it - sometimes. :(
I would say you are pretty normal, dont need to tell you what you need to do when you get an erection, I have had to do it in the privacy of a shower cubical several times, I am not gay either, wouldnt make any difference if I was, amazing what the body does when you work out.