You are correct, he is not to blame , having said that, was he meant to
tile around the window reveal and ledge, because that should have been tiled/grouted and silicone sealed before any water was allowed anywhere near that window opening. Back to the install, the
tiler has tiled and left a small opening for cable and water supply around these points, exactly as he/she is supposed to do , as is normal. he /she didn't plan this install, it was already done before
tiler arrived on the scene ok he/she could have cut
tiles to fit closer to entry point of said cable and pipe, however plumber /electrician should have noticed this when plumbing/installing/wiring said unit and rectified or reported this Or had a quick word with
tiler to fill said hole with grout/silicone Or they could have requested that
tile be removed and re-cut before shower unit was installed, thus eliminating possible ingress of water. Of course they didn't, they are probably on price work and were 20 flats away by the time you noticed it. This whole bodge is down to the person who planned the shower install and the contractor/s who agreed and carried out this typical council bodge. The council don't care if it looks ugly and will only last 6 months, as long as they can fill in a form to say 'property upgraded ', They Just Don't Care.