That isn't a LM mockup
According to NASM's website, that LM was intended for actual flight in Earth orbit but wasn't used because the earlier test went off perfectly (Apollo 9, I suppose, but it could've been an unmanned test flight like Apollo 6). It was an early production model that was too heavy to send to the moon. Even the Apollo 10 LM was too heavy to land on the moon. The Eagle was the first LM light enough for a landing.