Generally an industrial plant is a place where some industrial process occurs, such as making rubber baby buggy bumpers or retroencabulators or bubblegum. If an industrial plant happens to run generators to make its own electricity to power the industrial process, then it isn't a power company. It is an industrial plant that happens to use generators and is governed by the NEC.
A power company runs generator and distribution infrastructure to distribute electricity to customers. A generation facility might be considered a specific type of industrial plant, but the key feature is producing electricity that is sold to customers, not producing electricity for self use. The NESC applies to power companies.
-Jon