It's not uncommon for multiple technologies to unlock the same thing. For example, in the base game, both Construction robots and Logistic robots unlock the Roboport, and some of the chests.
Since the Heatpipe is both an intermediate(required to craft it), and a critical part of the heat power process (like power poles are for electric, and pipes are for steam and fluid power), and the tree has multiple branches that do not depend on each other (Doesn't matter if you have the burner heat source, oil burning heat source, or nuclear powerplant. and although currently the heat exchanger is the only thing that uses heat power, it might not be in the future), it's not unreasonable for each path to unlock the required heatpipes.
The nuclear reactor currently doesn't unlock any heat pipes because the heat exchanger is a prerequisite, and that unlocks them. (though it doesn't need to be a prerequisite from what I previously said)
