It’s possible.
I’m from the NE (NY/NJ), but lived most of my life in the south. I have zero NJ/NY accent even when I go back and visit the family (the conversations tend to be like My Cousin Vinny accent wise). I’ve lived in the south a LONG time and I’ve completely shed any accent I previously had.
I’m in the minority on here and I think BG is young, like currently 18-22. I don’t know that he’d have time to completely shed an accent so you could be right.
TBH I don’t hear any accent at all when I listen to the audio.
Im getting accent-topic reader fatigue but can’t stop myself from reading and writing about it.

1) Yep, agreed. I don’t hear an accent. And, if BG has one, that he actually uses, the sound clip isn’t long enough for us to clearly determine.
2) LE, more than likely, has a much larger voice sample.
3) Linguistics is important, but not an exact science.
4) Accents are so easily manipulated. I was born in the Bronx, and have lived in other locations/states, and while my whole family has an accent, I don’t. It’s partially effected by my age when we moved and where we moved, yet purposeful as a teenager and adult.
Maybe these are more easily recognizable accents, so this is not earth-shattering and impressive expertise, but I can clearly recognize regional accents in NH and MA (outside of Boston, Boston, and South Boston), South Philly, PA in general; and of course the general Southern accent, the deep-South, general mid-west accent, WI and NE, but not mid-west region specific.
All that said, it’s important. For example, in the new murder investigation from last week in Anchorage, Alaska, LE said they recognized the offender’s voiced, primarily due to his obvious South African accent. (I’m not linking due to time constraint.)