Who in there right mind wouldn't win the popular vote if could do it? Trump isn't making any sense here.
He's making perfect sense. You can't win the presidency by just winning the popular vote. (see Hillary)
You have to win the electoral college. Knowing full well he couldn't flip California, New York, Oregon or Washington, why would he waste a single dollar or a moment of his time campaigning in such states?
He also didn't need to spend much time campaigning in states like Texas, Oklahoma, or Utah. He was going to win those.
The way the system is set up, the only states that matter are "Battleground" states. Meaning Ohio, Florida, Pennsylvania. These and a few potential others, was where he needed to concentrate his advertising dollars and appearances. These are where he needed to concentrate his get out the vote efforts.
Donald Trump won the Presidency while spending less than half (I've seen even lower estimates) the money that Hillary spent, because he focused his efforts efficiently.
He ran a campaign like a businessmen, rather than like a government bureaucrat, and that's why it came in successful, and far under the budget that Hillary spent. (And that's not counting all the free positive publicity that the media gave her.)
If he was going for the "Popular vote", he would have spent more dollars and campaign time in New York and California, but that is not how the system is set up to award the Presidency.