As far as displays of poor workmanship goes this doesnt make that list at all. Yes it could have been done abit better (and ALOT worse) but at the end of the day its all about working gas pressure at boiler. Without adequate pressure your boiler cant be signed off. So many boilers are put in these days with no regards to gas pipe and pressure. Money down the drain.
If the layout looks that bad then it absolutely does, we can all make an educated guess as to why this particular plumber opted to do this but we also know how little extra it would've taken to do it properly and there's little excuse for that.