That’s why I said it was “confused” and that you don’t normally “pull a warning.”
The sentence should read either:
...pulled a “trigger warning” for two consecutive years.
...pulled a “trigger,” [issuing a] warning for two consecutive years.
Without a comma, the only way I see to read it is that trigger warning is a single lexical unit, with the trigger placed in quotes because that’s the element of new jargon.
I see it as an instance where the writer and editors didn’t exactly know how to parse this new phrase. Either that or the writer tried to get cute with the verb pull and just messed the sentence up.