You dumb asses need to learn the difference between "Membership" and "Access".
The term used was neither 'member' nor 'access', but 'still part of' - that is clearer more aligned with membership than mere access, noting that pretty well every country on the planet has 'access' to the single market - albeit in most cases with tariffs and non tariff barriers. I suspect the only countries without access are those where there are sanctions - so perhaps North Korea and a tiny number of other pariah states.
And note the word 'still' - in other words remain a member of.
The official Leave campaign clearly stated that we would 'still be part of' the free trade zone extending from Iceland to the Russian border - i.e. the single market/customs union. That was clearly a lie as we will no longer be part of that free trade zone.