They have subspace radio. Obviously they transmitted the specs for how to build the technology. It's not like the Hirogen are primitive. They were a warp-capable power in the 14th century. They're more advanced than we are. The only reason they hadn't invented holographic technology already is that they didn't want to, not that they weren't capable of creating it once they had the incentive. All they needed was the blueprints, so to speak, and they could've built their own. Yes, obviously, but that does not make it correct to use the word "serialization" to refer to ALL forms of continuity. DS9 was an episodic show that occasionally experimented with serialization. That does not make it a serialized show. Yes, of course an episodic show can have serialized elements. Again, that does not mean serialization is a synonym for continuity.