No, that's the engineers fault since that pipe wasn't leaking until the engineer unscrewed it. His action of unscrewing it literally caused the new leak. I actually saw him unscrew that area, then a gush of water sprayed out and he quickly screwed it back - right at the start of the job. He obviously didn't screw it back tight enough.
This may be difficult for you to understand.
The engineer unscrewed "something". Its not clear exactly what was unscrewed.
He then screwed "it" back.
It then leaked afterwards.
Now the difficult part.
You blame the engineer, not obviously why.
But could you understand if the engineer correctly unscrewed and screwed but the poorly matched parts did not seal properly afterwards?