He found out about the attack already in chapter 76, so entirety of 77 he was obviously monitoring the intruder. But even if we had not seen that, the mere fact that he noticed the intruder means that he must have monitored the room or people. Otherwise he wouldn't have noticed it.
Or, as I said, THE WHOLE BUILDING? The guy literally exploded a wall to make his way in, there's nothing suggesting that ONLY if Haruto had the barrier watching inside would he have known about the intruder.
Yes it is an assumption - because he has proven to have a habit of voyeuring ppl around him and had a really strong incentive to monitor it. And no, my suggestion doesn't imply he is ok with it. My suggestion disparages him for not caring about it.
Said people around him has been his family and servants, either the people he want to protect or making sure they're not causing problems.
Principal and Mer belongs to neither category in his eyes.
There's also evidences of him NOT constantly stalking people with his barrier.
The queen for one, he would've known about the capital attack plan much earlier if he'd actually been constantly watching.
So maybe you're just making shit up in your head and falsely blaming him for things he didn't do.