First off I do agree with you that this calligraphy illusion fails due to insufficient ambiguity of the "n" and "l" as you explained.
As for the audio illusion, I disagree with the explanation presented in that video. The sound's waveform is distinctly its own, regardless if it started off as "Laurel." It is both names, not one or the other.
For a more technical explanation, this audio engineer shows that the sound is composed of two distinct waveforms spliced together. There is a lack of harmonics from either section in the other part of the recording, which debunks the idea of "just 'Laurel' with added noise on top."
Your perception can be biased one way or the other based on equipment, age, etc. as your link shows. However it was disingenuous to claim "Laurel" is the one, correct "final answer." Their explanation would be like taking red light, adding in green light, then pointing to the combined yellow and saying "this is the color red" simply because "red is what we started with."
I'd suggest the wholly accurate answer is something akin to quantum mechanics and entanglement: it is both and neither, only manifesting one or another when we try to measure it with our perception.