Being Lead Developer in a one person team definitely sounds reasonable. You are still the lead dev on the project and have to take on all the responsiblities (even more so than if the team was bigger?).
To me even technical leadership still implies there are people that are less technically advanced that follow or benefit from the leadership. In general any leader implies followers, otherwise, what are you leading?
Note that I didn't say manage other people. I'm talking about helping get the better of the team, showing a junior member how things can be done better, etc. Like a team captain, not a coach.
I've never interpreted it as meaning leading people but rather leading the development of a project (or some portion of it). In fact, at IBM, I saw teams have multiple lead devs.
