Evidently the added words are those of a narrator as they do not correspond to the main topic in the previous sentence. However, even if the words are those of Prophet SAW, what is there to be explained?

—

Narrated Abu Huraira:

That he heard Allah’s Messenger (ﷺ) saying, “We (Muslims) are the last (to come) but (will be) the foremost (on the Day of Resurrection).” And added, “If someone is peeping (looking secretly) into your house without your permission, and you throw a stone at him and destroy his eyes, there will be no blame on you.”

حَدَّثَنَا أَبُو الْيَمَانِ، أَخْبَرَنَا شُعَيْبٌ، حَدَّثَنَا أَبُو الزِّنَادِ، أَنَّ الأَعْرَجَ، حَدَّثَهُ أَنَّهُ، سَمِعَ أَبَا هُرَيْرَةَ، يَقُولُ إِنَّهُ سَمِعَ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ ‏”‏ نَحْنُ الآخِرُونَ السَّابِقُونَ يَوْمَ الْقِيَامَةِ ‏”‏‏.‏ وَبِإِسْنَادِهِ ‏”‏ لَوِ اطَّلَعَ فِي بَيْتِكَ أَحَدٌ وَلَمْ تَأْذَنْ لَهُ، خَذَفْتَهُ بِحَصَاةٍ فَفَقَأْتَ عَيْنَهُ، مَا كَانَ عَلَيْكَ مِنْ جُنَاحٍ ‏”‏‏.‏

Reference : Sahih al-Bukhari 6887, 6888

In-book reference : Book 87, Hadith 26

USC-MSA web (English) reference : Vol. 9, Book 83, Hadith 26

https://sunnah.com/bukhari:6887

It is not a punishment and there is no encouragement to necessarily destroy the intruder’s eye. What is said is that even if the intruder’s eye gets destroyed in stopping the intrusion, there will be no blame on the house owner. It is a universally accepted principle that comes under trespassing, tort, privacy, and self defense laws.