In what region could one refer to honking a car's horn as "hooting"?
In English, to hoot or toot a horn goes back to the 13th C. I do not think any region can claim ownership.
hoot OED verb
To shout, call out, make an inarticulate vocal noise; to toot with a horn
As in:
a1225 [implied in: Juliana 52] Ne make bu me nawt men to huting ant to hokere. (at hooting n. a)].
More recent from google books (and there are many more):
I did hear a car hooting, but I honestly thought it was out in the road.