Trump's maybe dumb enough to think it's a legit offer. McConnell has to be looking at this as PR leverage. Dems have been able to say that they're passing bills in the House to open the government, that he's not allowing a vote on a bill which already passed the Senate at the end of the lame duck session, etc.
The media has a very strong both-sides tendency to describe these sorts of impasses, so the idea is to make a show of wanting to compromise even if it's bullshit. I don't think it's going to work, but can't blame him for trying.