because Im having trouble figuring out the Easter egg with a spartan marine
and seeing as this is sparta was a quote from 300
I looked up the film 300, and i noticed that it was released in 2006. When i looked up Halo 3 it’s date is listed as 2007, so that would explain why it would have the quote from 300 
It’s one of the funnier quotes from the game, thats for sure lol.
Hope that was able to answer your question
I remember watching 300 on DVD when waiting for Halo 3 to come out, if that helps you.
Definitely after, and yes, that’s where the line comes from.