From the Haydock Commentary, a meaning that I also just learned:
V. 24 Man, &c. By this one man is meant the whole Jewish people, out of whom the unclean spirit had been driven by the law. S. Ambrose. — For as long as they were in Egypt, they lived after the manners of the Egyptians, and were the habitation of the unclean spirit; but it was expelled from them, when they slew the paschal lamb in figure of Christ, and escaped destruction by sprinkling themselves with its blood. S. Cyril ex Divo Thoma. — But the evil spirit returned to his former habitation, the Jews, because he saw them devoid of virtue, barren, and open for his reception. And their latter state is worse than their former; for more wicked demons possessed the breasts of the Jews than before. Then they raged against the prophets only; but now they persecute the Lord himself of the prophets: therefore have they suffered much greater extremities from Vespasian and Titus, than from Egypt and Babylon; for besides being deprived of the merciful protection of Providence, which before watched over them, they are destitute of all grace, and delivered up to a more poignant misery, and a more cruel tyranny of the devil. S. Chrys. hom. xliv. on S. Matt.
V. 26 The last state, &c. But these words are also addressed to us Christians, who may often, and with reason, fear lest the vice we think extinguished in us, again return and seize on our slothful and careless souls, finding them cleansed indeed from the filth of sin by the grace of baptism, but destitute of every ornamental and protective virtue. It brings with it seven other evil spirits, by which we must understand every vicious inclination. V. Bede. — The latter state of these souls is worse than the former; because having been delivered from all former sins, and adorned with grace, if they again return to their iniquities a much more grievous punishment will be due for every subsequent crime. S. Chrys. hom. xliv. on S. Matt.
It seems that, since it was a parable, it has many layers of meaning - but those listening to Him could/should/would have known of where He spoke.