> The mall had a (most likely gas) explosion

If the internet searches are to be believed, that is indeed sadly likely to be the cause.

The internet suggests the explosion happened on the second floor of the mall where a large food court is located.

This article has confirmation that there was a report of a gas leak, and if you scroll down there is a dashcam video of the explosion https://news.web.nhk/newsweb/na/na-k10015188721000