First of all, quit being obtuse.
Second, train engineers are not the "original" engineers. The original engineers were people who designed siege engines (hence the name) for warfare -- ballistas, trebuchets, battering rams, etc. -- as well as fortifications. Military engineers predate trains by several thousand years.
Third, the second-oldest type of engineering is "civil engineering," and is named such because "civil" is the opposite of "military." Civil engineering is also several thousand years older than trains.
Oh, and by the way: the word "engine" didn't originally have anything to do with internal or external combustion; the Latin root word translates roughly as "a produced thing," or an object created by ingenuity. So in the truest sense, an engineer is anyone who uses his ingenuity to build something.
The only reason railroad engineers are called such is because presumably the earliest ones built the damn locomotive as well as operated it. Besides, the US and Canada are the only places that call people who drive trains "engineers" anyway -- everywhere else calls them "drivers," "operators" or "pilots."