Hi dowzer, I have had a look at the necklaces that you mentioned- all of the strands have been "finished off" via the pearls with thread, definitely no cable used, including the one with the “end caps”.
The caps look like they have a top ring to hold the chain, with a bar inside to enable the stringer to finish off via the pearls.
As for not being able to see any knots, there are various techniques for creating hidden knots - I know of two techniques. Alternatively it could be an unknotted strand, yes this is safe when done properly.
You cannot easily tell by the finished necklace the specific type of thread used. BUT - if this style of necklace came to my work bench for stringing, I would be able to tell if the thread was either silk, polyester or nylon thread. ( Tis an experience thing)
Paspaley are very proud of their in-house stringing technique - which does include the use of hidden knots. They also offer their customers a free of charge annual restringing service.