Comment by hansvm

IPA makes these conversations less ambiguous. The point is that parts of the South are more likely to use an "ah" sound rather than an "oh" sound in certain places. The BBC's example (supposing it's in good faith) is lacking because it drops the second half of the dipthong following that morphed vowel.

Attempting to write out something close to what I'm imagining they're trying to get across in plain English:

hell-ah-ooh

It's obviously not universal across the South, but you'll rarely see it outside of the South, so "might suggest you're from..." is probably accurate.