So you are arguing that the width is immaterial and that the boards were sold by the linear foot, not by the area?
OK, I can buy that.
What IS suspicious about this question is that the price is ridiculously high for 1895, and looks more like a current price.
$3901.44 would be about 9 years worth of average wages in 1895. Seems a little steep for 640 sq ft of planking!
well you could always have cut your own lumber, its not like there was a home depot in every town