[Sic] does not necessarily denote an error, because taken literally it means "thus," short for "thus was it written." It denotes specifically that you've put the original author's or speaker's text there completely unchanged, and you're sure that you haven't made any mistakes transcribing it.
However, I think that @sumelic and @StoneyB have it right here; ironically, the journalist made an error in examining the original text in placing the marker. I've said it on this site before, but journalists are quite liable to grammar and usage mistakes, more so than many seem to think. Their top priority isn't writing a piece that's completely free of errors, it's writing one that becomes popular. At times, that priority will even be at odds with proper grammar. Maybe the journalist will use some piece of language that is known to be incorrect, but it is currently trending.