The Nasal thing also goes for people who can speak any Asian (non-indian) language. You can tell it's an Asian person speaking even if you don't see them.
I think it comes down to Richard. Whether he's in on the gag or not, he bears such a perfect look of deadpan, Windows 95 blue screen of doom error that silently says "...are y- are you-........actually gd serious right now 😐". It's so real and believable for him, both out of character, and in his usual character as a polite but very awkward, constant smartass. This kind of silly thing happens irl all the time, there always is that one guy blissfully unaware of his flaws or strange voice, and so this isn't too unbelievably weird a scenario to guess is real. ....On the other hand. It's a comedic talk show host. 🤷 Clearly gonna take every chance he gets to make the audience laugh at himself.
You don't breathe through your oesophagus. You breathe through your trachea. And what would lead to your voice being more nasal would be something to do with your soft palate, which controls the airflow through your nose when speaking.
I think this is the first time I’ve heard this Alan guy speak (I haven’t seen the show and this is the first clip I’ve come across) and I genuinely thought he was faking his voice at the start. “Okay he’s doing a bit………… oh wait no..”
Interestingly, your voice is not just a function of the mechanics of your throat, nose, and sinuses, but how you use those organs. If you were to be "wiped" and taught to speak by entirely different people, you would probably sound somewhat different.