The article said he worked 1992 hours of overtime for an average of 78 hours per week. If the wage breakdown is accurate, then he must have had a salaried position with a contract that pays straight time for overtime. if that is the case though, there isn't really any benefit to hiring another worker.
Another possibility with a report like this is that the "normal salary" was his total base compensation, including healthcare, retirement, etc. It's not unusual to see an extra 40-50% in benefits cost (I've seen new hires start at +60% because of a lower salary magnifying the healthcare and other fixed benefits but drop slowly as salary goes up, but retirement cost tracks increasing salary).
So a base salary around $165k +41.2% benefits cost would give you the 234,407 base while also giving an hourly rate of $79.45 or so on a normal 2080 hour work year. That at 1.5X OT rate happens to line up almost exactly with his reported OT earnings and hours.
And if they are an experienced engineer working in a technical field in a high cost of living area like NYC, $80/hr is not astronomical. From my experience, stationary engineers can either start on small equipment, pressure vessels like pumps, boilers, compressors etc. with some trade schooling and progress up in steps over many years to the largest industrial equipment. Or they can get a bachelors in mechanical engineering or similar and progress directly to larger equipment with a shorter term under supervision. Either way you end up paying for their schooling and/or experience.
<- government worker whose salary shows up in news publications from time to time.