What does this mean?
This means you can title your extension name with the same name as a 3rd party library. But you can not title your eSpace name with the same name as a 3rd party library (this will cause conflicts and odd behaviour)
As for running multiple extensions with different version of a 3rd party library! there is a work around for this but its not recommended. (way too much work!)
You might run into issue if you consume many RESTful web services via extensions instead of using the built in outsystems service studio REST consume feature - because there is a high chance you would reference multiple versions of the same commonly used libraries json.net, RestSharp.net etc! - So it's best for you to consume a web service via outsystem service studio - REST consume! (This would not eliminate the problem but it sure would reduce some common issues)