Congratulation on your first post.
A remarkable topic to start out with.
Well, IMO it's more likely a mistake.
The average height for women in that period would have been around 150-155 cm. For nobles, and other well to do, the average height for men and women would have been a little higher, due to better nutrition and slightly better living conditions.
That means Matilda would have been at least 20 cm below the average height!
Even at that time she would unquestionably have been labelled a "dwarf". - With all the stigma that followed I find it unlikely that the Duke of Normandy, a very important man regionally, would have married what he and his peers would have called a "freak" behind her back. - Why, she would likely give births to "freaks" rather than big strong sons and what duke would want that?
That William was able to carry his wife on his shoulders, doesn't impress me.
He was a strong, fit man, who was physically active for most of his life - like most other men of the warrior class.
It would surprise me if he couldn't!
She might very well have been slender and/or below average height at the time, but not that short.