Technically a multi-line hologram doesn't exist. The multiline command just creates multiple holograms in a specific distance to each other. This can be seen when you execute the list command. A multiline hologram appears as many single holograms. The plugin doesn't even know that this is a multiline hologram, they are just perfectly placed on top of each other.
Well, no. There is some space between the holograms and that can be calculated by the plugin. Teleporting to a specific line is just for the purpose of selecting the line. If there aren't many holograms around, the player doesn't even have to teleport, he can just stand near the hologram.