Is because there is more people in the server than it can show. It absolutely HAS to show you, so it shows you in a separate section.
If enough people are playing, it will not show all the spectators, and all the players on the losing team. So, if you were on the bottom of the list on the losing team, you would also be put in separately like you were in your screenshot. This would kinda make it appear as though you are specing, when really you are just on the losing team.
As far as the server is concerned, it views the scoreboard as a linear list: "winning team, losing team, spectators"
each sub list is in order of score/points. When there is a tie there(or if your speccing) then I am not sure how it orders the list, maybe order of joining the server.
So, if there is more people in the server than the scoreboard can fit, it leaves them out.
It is not allowed to leave you out, so it gives you a special, separated spot at the bottom
keep in mind, that this 'leaving players out of the scoreboard' can make it seem like the losing team has considerable less players than the winning team, when actually both teams are even.
hope I explained it good enough ^_^
