Whether a source is primary depends on your question

A primary source is firsthand evidence from the time or subject under study. A secondary source interprets that evidence. The label describes a relationship to a question, not the document itself. An article written in 2020 about the 1918 influenza is secondary if you're studying the pandemic, and primary if you're studying how people wrote about it in 2020. Before calling a source primary in a note, say which question it's primary for.