Rubbish, pure and simple.
If anyone has any experience of negotiations whatsoever, they understand that people set out all sorts of demands at the outset which they concede later on. Of course they only do this if/when they have to, in order to secure a deal. And they will do not so, if they can get away with out it. This is blindingly obvious. Which is why the Benn ("Bean" would have been a more apt term) legislation preventing no deal, was so utterly idiotic.
If Johnson wins the GE, he will set out on the same tack as he did with the October 31st deadline. He will be saying we are out come what may by <date> and no matter what we are leaving on that date, on WTO terms if necessary. And the EU will cave in on all sorts of things, because they absolutely DO NOT want an economy like Singapore 26 miles off the coast of France, able to cut corporation tax, cut VAT, cut EU legislation and able to offer all sorts of incentives for foreign investors to come to the UK and not the EU.
Are the EU going to admit this now? Of course not, don't be ridiculous. The twitter post we are talking about here was ludicrous and pure political spin. Nothing more.