He's probably talking about structures like this one at Senam Semana in Roman Tripolitania:
You can see the superficial resemblance to the Stonehenge trilithons:
So it is, perhaps, understandable that nineteenth-century travellers in north‐west Libya took them to be prehistoric megaliths and assumed they were of ritual significance.
An extensive study was carried out by H. S Cowper and published as The Hill Of The Graces in 1897. This includes descriptions and photographs of many of these structures.
A possible reconstruction of one of these presses is shown in figure 17 of An Archaeological and Historical Guide to the pre-Islamic Antiquities of Tripolitania by D.E.L. Haynes:
He describes the presses thus:
"The olives were placed in a perforated container on a stone slab draining into an adjacent tank. On top of them rested a plunger attached to a long wooden lever, the butt end of which was held down by a wooden bar secured in holes or slots between two massive pillars of stone. The free end of the lever was then drawn down by a windlass or pulley anchored to a heavy block of stone sunk in the ground. The two pillars, which usually constitute the most conspicuous remains of a press, were ten or more feet high, and might be either monolithic or composed of several blocks. They were set close together on a single base and joined across the top by a stone lintel, on which other blocks were often placed to add to the weight..."
The size of the structures is simply a reflection of the scale of production at these presses
The function and operation of the presses is discussed in D.J Mattingley's Megalithic madness and measurement. Or how many olives could an olive press press?, published in the Oxford Journal of Archaeology (Volume 7, Issue 2, July 1988, pp 177-195)