The key to that parable is that the clean house means that the person has not filled his house with the Holy Spirit so it is subject to repossession.
But the follow up question is whether a man can be a Christian believer without being filled with the Holy Spirit. And this is shown to be the case.
Paul met several congregations where they had been baptized as believers but had not yet been filled. Were they fair game for demon possession?
Except that every believer does have the Holy Spirit indwelling him so the house is not swept clean. it now has the presence of God in it.
However, through sin and unforgiveness, the believer can give the enemy a foothold to operate from so that he experiences demonic attack within.