That's an interesting perspective. I think it's still a bit of both. Yes, GOP has been shifting away from small-government, balanced budgets, and free trade, leaving the Libertarian platform to pick up those staunch proponents. However, the socially liberal aspects of the Libertarian party, like drug decriminalization, criminal justice reform, and gay marriage have been cornerstones of Libertarianism and Republicans would still be crossing over on those issues that haven't been a part of the historical Republican base. Another interesting difference is that the current Libertarian nominee's environmental platform is based on Nuclear, solar, and other renewables[0], in contrast to Republicans' usual Oil and Gas position.

[0]https://jo20.com/issues/environment/