This may well be technology and terminology that morphs over time.

Hollowtech was Shimano's big thing with the Octalink.
Then with the external bottom brackets, they would have introduced the 24mm 2 piece cranksets with "Hollowtech II". Initially these would have been exclusively Dura Ace and Ultegra.

I know that Claris got Octalink V2, which was used for several years.

When was the Tiagra 2-piece introduced? I presume the Hollowtech II had been in use several years before the Tiagra was converted to that technology (without the hollow).