Does "being ghosted" mean "rejection" after PhD interview?
It could be that unforeseen circumstances have prevented a timely decision. However, most likely you are not their first choice but they don't send out rejections before their first choice has signed the contract. That's pretty standard.
Something similar happened to me in the past. Three months later they called me and asked if I would still be interested. Their first choice had decided against the position. If they had send out rejection letters they would have had to restart the whole process again (with a new job posting).