Trust us ! There is no such thing as a one pin LED, actually i can't think of any electronic componet having less than two (or more) pins
The other pin is hidden under the LED, it's the angle the picture is taken at that hides it.
Thr other pin from each LED is connected to the same row of holes in the breadboard as the resistors.
Which is why circuit diagrams are better than photos when building your own circuits!
I appreciate they do make it harder for beginners, but perhaps it would help avoid such errors.