No, it's not hard to believe at all -- it's perfectly logical, although I think the terminology may be getting confused here.  I believe by "Engineering" units Biker Chick must be referring to typical Civil Engineering or Surveyor CAD-drafting practice, not to what AutoCAD calls "Engineering units" for length.  In both Architectural and [AutoCAD's definition of] Engineering units, the drawing unit is an inch, which is the only way they can get feet and inches in Dimension text, allow them for user input, etc. -- the difference between them is only in portions of inches [fractions in Architectural, decimals in Engineering].  But Civil Engineers and Surveyors typically use a foot as a drawing unit, and use what AutoCAD calls Decimal units for length.  A building that's 100 feet long is, in Architectural or [AutoCAD's] Engineering units, 1200 drawing units long.  AutoCAD's drawing file format stores that size in "pure" drawing units, unaffected by what your Units settings are.  When you import an Architect's drawing like that into a Civil Engineer's or Surveyor's drawing in which the drawing unit is a foot, it will still be 1200 drawing units long, which will come into that drawing as 1200 feet long, exactly as described, and it will need to be scaled down.  We do this all the time, except in the other direction: we're Architects, so we scale up drawings we get from Civil Engineers, because their 100-foot building would be 100 drawing units long, which, unscaled, comes into our drawing as only 8'-4".