Agree, if shower manufacturers allow top entry for pipe and cables, it must be safe to do so.
Not to mention the IP rating of trunking I know it’s not singles but stillDid he arrive on a horse? That’s appalling. He has negated the IP rating of the shower.
Water will get in, it will cause problems.
I really hope you haven’t paid him.
But only if the manufacturers instructions say it’s ok because many don’t allow top entryI believe that what they have internally where the cable entries are is like a trunking type effect that separates the entry point from the internal electricals, so if water does get it, it runs down inside the cavity and drips off harmlessly into the bottom of the case where it can then run out.