Believable. He sounded kind of jaded when talking about continuing earlier this season. Charges looming. The team he's got now is at its peak, but the next step will be to replace it and that will require a couple of seasons to push through. His old rival Klopp has stepped away. Lots of good reasons to think this might feel like the right moment.
Of course, until he actually goes, he could change his mind at any point. So even if it's true that he intends to leave, it's far from certain it'll go through. But at the end of the day, he'll leave eventually. Seems as feasible a time as any.