When you fly from overseas destinations to the USA on US-based airlines, you ordinarily clear airport security and supplemental security provided by the airline.

In most cases this involves an interview prior to check-in (this is where the sticker goes on your passport), a checked bag inspection (with stickers on your bags), and an interview immediately prior to boarding.

The interviews are conducted typically by contract agencies, such as ICTS or Securitas. The agents either wear uniforms of the contractor or airline uniforms. They also set up "kiosks" for the interviews that usually say "Delta Security," "United Security," etc.

Some stations are more stringent than others. I'm surprised that you did not undergo an interview in Bogotá.