I wouldn't be ashamed, others are right they could have closed the blinds, all you were doing is looking out the window. I think if you feel bad about it, and feel like you're violating their privacy, then just choose not to watch them again. And certainly just glancing out your window is different then trying to seek it out, as others have said.
Personally I don't really want to see other people having sex in their private space, I just think that's none of my business. I think I have a pretty high desire to have boundaries respected in a lot of ways. I will admit that once I was in a hotel room that I was staying for a friend's wedding, and I started to hear a rhythmic shaking, then realized oh k, I think the people next door might be getting busy. I wasn't quite sure that's what the noise really was, and in all seriousness my thought was is it really that easy to hear into the next hotel room? So I pressed my ear up against the wall, and let me say that not only IS it that easy to hear into the next room, but I was shocked how when I put my ear right up to the wall, it was almost like there was no wall. I could hear that clearly, which was a little disturbing, and yes, all of a sudden it was completely clear that indeed the rhythmic thumping I'd heard was a guy, for lack of a better term, thoroughly giving it to a woman, and her either 1. in need of rescue, or 2. enjoying it thoroughly. My next thought was I wonder if I'll see them leaving their room or something tomorrow to see what they look like lol. Then I went back to my book in the chair and left them to their fun. The thumping lasted a few more minutes then stopped, and no I never saw them the next day.
I don't know, was just a funny story lol.