Confirmation

From

The From clause is in essence a filter on resource type.

from Patient
select 
    id,
    name.family,
    name.given

The above statement effectively selects all patient records in scope, which could be all patients of the entire server.

Bandwidth

When requesting data from a FHIR server, the from clause is also mapped to a search query to reduce bandwith and increase performance, like this:

using 'https://vonk.fire.ly'
from Patient
select 
    ...

The from Patient clause here is translated to a FHIR search request URL to the FHIR server: http://server.org/fhir/Patient.