From the acknowledgment at the end, I guess the author has access to TPUs through https://sites.research.google/trc/about/

This is not the only way though. TPUs are available to companies operating on GCP as an alternative to GPUs with a different price/performance point. That is another way to get hands-on experience with TPUs.

A quick free way to access TPUs is through https://colab.research.google.com, Runtime / Change Runtime Type / v2-8 TPU