I fixed it without figuring it out. What didn't work is copying the table into a new document. The same strange page dimensions persisted. Then I copied the whole document into Excel, changed the cell widths etc, then pasted it back into a new Word document and the page size was correct. I sort of wish I new what the deal with my original document was so I can avoid the hassle in the future. The doc was sent from my client so I wasn't the author.