When a chemical loses a hydrogen ion, is it behaving as a chemical or a base? What is meant by "behaves as"?
It behaves as, which likely means that it fits into the definition for, a Bronsted-Lowry acid.
The Bronsted-Lowry acid-base theory defines acids as species that lose hydrogen ions (
"A Brønsted-Lowry acid is a proton (hydrogen ion) donor." 
The chemical in question here loses protons and fits into the definition for Bronsted-Lowry acids.
 Libretexts. “Brønsted Concept of Acids and Bases.” Chemistry LibreTexts, Libretexts, 21 July 2016, chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Acids_and_Bases/Acid/Bronsted_Concept_of_Acids_and_Bases