Matplotlib.pyplot sometimes understands CUDA Tensors, sometimes not. How?

fastai
1

When asked to plot a CUDA Tensor, matplotlib.pyplot complains
TypeError: can't convert CUDA tensor to numpy. Use Tensor.cpu() to copy the tensor to host memory first.

But after
from fastai_timeseries import *

matplotlib and scikit can handle CUDA Tensors directly.

Would someone kindly explain to me how this works?