That's not the driver, that's just the example.

However, according to the style guide, camelcase is preferred, and the compiler is supposed to generate language-native names with the correct case [1].

One thing the terrible years of SOAP and WSDL should have taught people is that generated stubs are awful to use if they go against the grain of the host language.

[1] https://developers.google.com/protocol-buffers/docs/style

Not great, but I think it is to match function from the protocol definition. Inside that function you can see "normal" looking python function get_feature.