Selenium Jmeter differences on websocket calls

I am researching the differences between Selenium and JMeter and I stumbled across the following statement about Selenium:

Even though WebSocket might be encapsulated into a web session and affect the browser, the user/Selenium will not realise it. So, we will use JMeter for testing WebSockets.

which confuses me because even though Selenium can't detect that specific scenario, Selenium still uses a programming language like JAVA, hence you can still use Java to accomplish the same thing JMeter does in this case. Or am I missing something here?