Going by the current stats available, the mountain has already spewed enough ash from January to July, amounting to twice the amount emitted in all of last year. Masato Iguchi, a professor at the Sakurajima Volcano Research Center said that last year saw a record number of eruptions as well. The ground around Sakurajima indicates the buildup of magma and appears swollen.
And if Sakurajima keeps being as active it is right now, we can expect the amount of ash expelled to be a new record. In the past two decades this year's activity of explosions and ash fall have both risen dramatically.
As a part of the Kyoto University's disaster reduction research institute, keeping a tab on such stats is imperative to avoid another Pompeii. You may recollect the 1914 eruption as one of the deadliest one that killed 58 people. Presently, Minamidake crater erupted last month for the first time in about a year and a half and the Showa crater has been active since 2008.
I think the original title is a little more accurate: Volcanic Mount Sakurajima estimated to spew most ash in two decades
The article makes it clear that it is not yet a fact that it will be the case, but it will be the case if the current activity continues.