About the ONNX file
The segmentation model was converted into ONNX by PINTO0309 (Katsuya Hyodo). Please check his model zoo for further details.
About the license
Even though the repository contains the original license (Apache 2.0), the developer (Google) changed it to Google Terms of Service after the initial release.
There are some threads trying to make it clear if we can use the model in commercial/non-commercial projects, but at the moment, there is no clear conclusion.
I'd recommend NOT using the model in practical applications. Please ask a lawyer for further advice.