I don't know if that counts as plagiarism, but there's clearly some use of this copyright material that the authors probably didn't envision and did not grant permission for. I have no idea what the law would be in cases like this
the data was originally permitted to be copied.
The question isn't whether the training is violating copyright - as long as the data set had permission to be viewed (which it must have, since it was public).
The question is whether the final result - the model/weights - is a derivative work of the training data set. If it is a derivative work, then the model must be in violation of copyright. But copyright law allows for sufficiently transformative work to be considered new, rather than derivative. So is training a model using methods like this constitute a transformative work?