It says earlier in the article that the volcano could warm the Earth noticeably

Other sources making that same claim:
https://eos.org/articles/tonga-eruption-may-temporarily-push-earth-closer-to-1-5c-of-warming

https://www.carbonbrief.org/tonga-volcano-eruption-raises-imminent-risk-of-temporary-1-5c-breach/

https://www.nytimes.com/2022/09/22/climate/tonga-volcano-climate.html


Here's a published paper saying it raised the atmospheric water vapor by 13%, this will last for years and will warm the surface:
https://communities.springernature.com/posts/hunga-tonga-eruption-the-most-remarkable-climatic-event-in-the-last-three-decades