You are right of course. I, as well as others, had interpreted the question and replied accordingly.
The reason is this: I have noticed that travellers from the USA write "clearing customs" but what they mean is "getting off my plane and boarding my connecting plane and what happens in between". Just in case that there are objections to my wording: This is
not national stereotyping, it is an observation, and I assume that it has to do with the fact that international airports in the USA are organised differently to those in the EU in this context, i.e. it has to do with what one is accustomed to when living in a specific geographical region.
I re-read a similar description just now from a traveller on a recent flight from the US to Pamplona with a change of planes in Madrid:
I cleared customs about 15-20 minutes after getting off the plane. Very fast. Found the airport tram downstairs. Took tram from T4s to T4 for domestic flight on Iberia. [...] then went to K gates [...for the flight to Pamplona]. It is obvious from this description that this traveller did not go through custom lanes. She went through passport control.
If
@steven mains would not mind sharing the names of the airlines for the flight from the US to Santiago, it would be clearer to us what he meant. From the way the question had been formulated I had also assumed that it will be a flight landing in Terminal 4 (i.e. T4/T4S).
I agree: When you have passed through the customs lane / customs corridor / customs area you are "outside".