The choice I made when building this, was to take the groupId as ${organization}-${project} so in here it would be org.lwjgl as the organization and lwjgl as the project.
This is not too pretty on the eyes when the project shares the name with the organization, but I think it is still better and makes it nicer if you ever add other projects under the umbrella of lwjgl.org, examples of that could be, if you split the appletloader into a separate project from lwjgl so org.lwjgl.appletloader would be the groupId, or anything else you may want to do.
In maven projects are usually made of different artifacts grouped under the same groupId.
In our games we usually have for example
groupId: com.gemserk.games.thecodenameofthegame
artifactsIds: thecodenameofthegame-core, thecodenameofthegame-android, thecodenameofthegame-desktop
Personally I have seen both decisions even from the maven guys, having multiple projects all share the same groupId using it only as the organization or as a category of stuff like org.maven.plugins and all the artifacts from the different projects live under the same groupID. Or using the groupId as the organization + projectName.