Well, let's take a look under the hood to see what's going on here.
The entire section from 5:14 (from the guitar slide) to the end would be considered the Coda. It's very short, only six measures long, but here's the play by play (note that the Chorus just before it is in G-major/C-Lydian, and that the song starts and ends in c#-minor/phrygian):
First four measures: the guitar and bass hammer away at C# to emphasize the new key center. There are other notes here (they hit the occasional Bs, and end the first/third measure with an E and the second/fourth measure with a D), but all of the C# notes are accented and its clearly the basis for the whole passage. The keyboards play a counterline which (to me at least) sounds like it's just alternating between C#5 and D5 twice on the second half of the riff. This riff also shows up a few times in the song (usually to transition from the chorus to some instrumental section), so there's already an expectation of what role this riff will play, which they kind of play off of here. The main thing to note is that the band ends this riff on a D, which sounds dissonant and needs resolution.
Fifth measure: a brief rest in 2/4, as opposed to the 4/4 that dominates the section. It lets the melodic dissonance "sit" in your head just long enough that the song doesn't feel totally unresolved at the end and leaves a bunch of tension (basically, without this pause you'd probably think "that's it?" at the end), but not long enough that you start feeling uncomfortable or the last measure feels like it comes out of nowhere. If you want a technical term for this measure, I've never seen one but "dramatic pause" seems to do quite nicely.
Final measure: back to the primary meter of 4/4, the band plays around a D5 for the first half, then ends on a C#5. This, to me at least, seems like some sort of melodic/modal cadence to resolve that dissonant D (that's what she said) back down to C#. It's a very metal thing to do.
Why tag this on at the end? Well, ending a song in a different key than you started in is...well, it's generally not a good idea. All art is based around this principle of "there and back again", where you start at home, go somewhere else and do the things, and then come back home again a little different at the end of your adventure. Without that last bit, the song would feel like it ended on a cliff hanger, with no sense of resolution. What will happen to our hero next? Will he ever make it back home to c# from the magical land of G-major/C-lydian? Tune in next time on-whoops the show's been cancelled. It's a little clunky, but it kind of sort of gets the job done.
So, tl;dr: it's a melodic/modal cadence following a dramatic pause in a brief coda section to return us to the original key center of c# so that the song doesn't end on a cliff-hanger.
There's no specific term for that brief measure at the end, which you'll sometimes come across in music theory. Sometimes the only thing you can do is to describe what's going on and venture a guess as to why it's happening. But, if you want a simple (if slightly less accurate) one-word definition it would be a
Coda.
I'm hung up on it though. Does it really count as a coda in this song? I'm probably overthinking it, since I'm envisioning classical music structure, but I suppose it's as valid as an extensive coda by Mozart, just much shorter and simply tacked on at the end.
In classical music, codas can vary in length from "literally nothing" or "like two to four measures of V - I" (more common in Classical and Baroque music) to "this is literally as long as the rest of the piece combined" (more common in Romantic music and late Beethoven). So, yes, it would still count as a Coda.