3-way switch wired with jumper between load and traveller
The traveler isn't really hot unless it's wired to something

That 26V you are measuring isn't a sign that some weird wiring is making the other traveler hot.  It's actually a phantom voltage caused by capacitive coupling from the wired traveler to the unwired traveler -- your meter is high-impedance enough to see it, but since only a tiny current can flow through the small inter-wire capacitance that is coupling this voltage over, it can't actually deliver power, and should be treated as not-live for wiring's sake.

Since you have the wires sorted out at this point, you should be able to wire the Caseta as a 3-way according to Lutron's instructions on the topic, which require connecting the mechanical switch at the other end from the junction of the load wire (ex-traveler) from the Caseta with the wire powering the load to the other ex-traveler, which then connects to the traveler wire on the Caseta itself, assuming you have a model of the Caseta that supports multi-way switching using a mechanical switch.