You need less hours to build a heavier boat, so that it's a coincidence those numbers are more or less alike.
A very effective building method rendering a light bout would again give you the same number.
The number is meaningless.

As it happens people have to make estimates like these all the time, those estimates are made as close as possible as they would be intended to direct the resources of human and cash capital to cover the tasks at hand. These days this is the province of Industrial Engineers formerly of time and motion analysis and among their tools methods of estimation not unlike those applied here.

Yes they can be wrong, we actually expect them to be 'right' only within a percentage of expectation, this is how we know that a ship build can be a year late and over budget, somebody somewhere made some estimates based upon the knowledge at hand.

Where in this case the boats are of similar design, with familiar layouts, endeavouring to deal with almost identical tasks, it is an easier probability than most.