This misses the point. Of course it is possible to build 53’ containers; you cannot ship them on conventional large trans-ocean container ships. The article you link makes this point specifically, and the company is offering containers for use as shelters.

You should really read the article. Ben is arguing that 53 foot containers exist, but not for ocean shipping, only land. The link you've posted says the same.

"The USA and Canada, however, have been using 53ft long containers for road and rail transport since 1989"