You had all of the photos highlighted so that you could synchronize the metadata. Double-clicking on the single image didn't cancel the highlight of all the other images. When you went into the export dialog all of the highlighted images were exported. If you want to cancel highlighting of multiple images you need to click in the gray border around the image. Clicking on the image itself will give focus to that image, but will not deselect the other images. The only "default" setting in this regard is that any images that are highlighted WILL be exported. You just need to watch a little closer
WOW. Thats different. I will have to watch it in lightroom.
What about adjustments? When all are highlighted and i focus on one are the adjustments happening to all? It doesn't look to be that way but i just want to be sure.
That depends. If you have auto-sync enabled then the adjustments will be applied to all images. That's another gotcha that has caught me a few times. In case you are unaware, when multiple images are selected there is a little switch to the left of the sync button that will allow you to enable auto-sync. I think it is best to turn it off when it isn't needed