That's then malecon in Mahahual, not Nuevo Mahahual.
@c-leg5 our taxi driver in January took a "shortcut" along a pot hole street that ran adjacent to the main drag out of port. We did pass a spot where it looked like you might be able to climb down to the beach, but it was overgrown and I would trust it to get all the way down and be able to walk to the lighthouse. From the pier, that whole route didn't look inviting.