It's only an EU passport in the sense that it has the words European Union on the front cover. It also has the words United Kingdom of Great Britain and Northern Ireland on the cover in a bigger font. Inside it has the following statement:
Her Britannic Majesty's Secretary of State Requests and Requires in the Name of Her Majesty all those whom it may concern to allow the bearer to pass freely without let or hindrance and to afford the bearer such assistance and protection as may be necessary.
It doesn't say "The EU Commissioner Request and Requires ....". It is issued in the UK by a UK agency on behalf of the UK government not in Brussels by a Commission agency on behalf of the Commission. The Commission does not have the right or authority to issue passports on behalf of any member state or of its own. When you enter the USA, for example, I can pretty much guarantee you that if you declared that you were a Citizen of the EU on your entry form you would not get in.
Also, as far as I can see, the idea is to grant residency rights not to issue people with passports.
To say the EU produces nothing and doesn't have a GDP is nonsense. It is true that "the Commission" doesn't have a GDP but the term EU doesn't mean "the Commission". The EU simply denotes all its member states. You could equally argue that the USA doesn't have a GDP only the individual federal states or Germany doesn't have a GDP only its independent federal states. Whenever the term "X GDP" is used it is simply the aggregate economic activity of the area specified by X. It is just as valid to talk about World GDP, or Asian GDP or South American GDP etc as it is to talk about Indian GDP or Australian GDP.