However, Richard Tice, co-chair of Leave Means Leave, said: "This report from the CBI protects the vested interests of global multi-nationals at the expense of the approximately 90% of the UK economy that does not export to the EU.

Does he not understand "the EU, the UK's largest trading partner." or is he just looking after the interests of the part of the economy that does not export?
I imagine he fully understands the term. "Largest trading partner" is the country (or bloc) with which we do the most trade. This includes both buying & selling. With the EU we buy more from them than we sell to them. As such it is in the interests of the EU not to hinder international trade.