If you want to restrict the definition of HFT to only sub-millisecond strategies you're correct. But then, all HFT is impossible in crypto, since with web request latency and rate limits, it would be very difficult to get tick speeds even in the 10s of milliseconds. It's fine if you want to call this "algo trading" instead of HFT, but I think a common understanding of the term would include Gryphon's capabilities.

In any case Gryphon uses Cython to compile itself down to C, which isn't quite as good as writing in native C but is a good chunk of the way there.