"The main difference between the two fluids is that Toyota CVT TC is designed for use in Toyota vehicles equipped with conventional CVT systems, while Toyota CVT FE is formulated for use in Toyota vehicles equipped with more advanced, fuel-efficient CVT systems."
This is quoted from a website. If you have proof they put TC instead of FE and are concerned about this, you may show said proof and argue them to change it out.
From some basic research, it seems FE is of less viscosity to improve fuel economy. However, do not quote me on this. I had trouble finding a straight answer form any research.