As he explained to me, yes, he did in fact break the glass himself to reach the lock and get in. And why? Well he had forgot his key and of course he could not stay outside in the cold (this was his explanation). I made it clear to him that the reasonable response to this situation would be to call a locksmith, and he replied that he forgot his cell phone inside - and this discussion with me upset him somewhat. He said he had already called the owner of the house and arranged for a glazier to come by soon and that he would pay for the damage.
I hope it is clear to you, dear reader, that there are several reasonable solutions to this apparent problem of being locked out *even* if you have no cell phone and *even* if your neighbour (me) is not home at the moment. Actually we happen to live next to a small shop (the place he had gone without his key) and for any likely situation the shopkeepers would be more than happy to be of help by letting you use their phone. The solution he chose: smashing in the window, actually leaves open the possibility for any person to walk up to our front door and let himself in.
Anyways, this afternoon I heard him and his buddy shouting at each other, tramping around the flat, turning up the music too loud, turning it down again, having a yes-no-yes- no-yes-no-argument and later both of them went out.
At least it will be quiet here until they return home.