@Andy26,
It's not a problem. This is how Facebook works. You can like either an individual image (by clicking on it and hitting like), or you can like someone's post of an album by liking the post or you can go straight to the album and like it. Both of the last two actions like the album (and all the images in it) rather than an individual image.
I strongly suspect you liked a person's post where they posted the album link. That got you liking the entire album. Next time, if it bothers you that much, click into the album and select individual images to like.