Each LED has four contacts on the bottom. When the solder melts, surface tension of the solder should pull those contacts into alignment with the pads on the bo

Each LED has four contacts on the bottom. When the solder melts, surface tension of the solder should pull those contacts into alignment with the pads on the board. I think what they're saying is that they they accidentally laid out the contacts in the wrong orientation, and needed to rotate the LED 90 degrees to put each contact on the appropriate pad. Because the arrangement of those pads is not quite a square, the LEDs do make the connections, but they don't get aligned quite straight.