He clearly yelling "Roona", i don't really know how people can hear "Stella" or even "Frena" here, lol.
It's an audio illusion. I've seen (technically heard) this a few times before.
We don't see or hear anything as it actually is. Our brains interpret things first. That's why, for example, the moon looks so much bigger when it's out on the horizon than it does when it's high in the sky. That's not some kind of refraction thing. It's 100% in your head, and you can prove it to yourself next time you see it by making a "telescope" with your hand and looking at the moon by itself, without the background. It will suddenly look as small as it would look if it's straight up in the sky. You brain sees something on the horizon, it tells your visual cortex that it's gotta be huge, and you literally see it bigger.
Or, like how someone who is deathly afraid of spiders looking at a spider saying it's huge when someone next to them sees it as a tiny thing. That heightened sense of danger makes your brain actually interpret the spider as larger than it is. It literally looks bigger to that person.
The same thing can happen with audio as well. A recent example is in MGSV. When you fulton soldiers, something Kaz says "You're going to extract him?" and different people hear different inflections. Sometimes I head "You're going to extract HIM??" And sometimes I hear it more like "oh, you're going to Extract him" but the audio is the same every time.
I imagine this is the same effect that is leading some people to see Arenea and Lightning as twins. And I think that's because these people don't have a particularly strong connection to one or either character, so their brains are only interpreting them at a superficial level. Once they see enough of Arenea to have her register as a different character, they'll never look alike to that person again.
Thus endeth today's episode of nobody truly knows how much they don't know!