Yes he is an outside contributor with conservative bona fides. But the fact that he uses liberal or neutral sources for his numbers counters the argument that this piece is ideologically slanted.

As to the rest of your criticism, what is sloppy and misleading about the following?

"To begin with the necessary context: The Congressional Budget Office (CBO) assumes a baseline budget deficit of $12.4 trillion over the next decade (assuming current laws continue). And even these projections assume that last year’s tax cuts expire on schedule, though they may well be renewed, and that the recent two-year discretionary spending hike is not renewed in 2020. Most of this deficit is driven by the escalating Social Security and Medicare system deficits."

He's saying that per the CBO, the budget deficit for the next decade will be 12.4 trillion without these new socialist programs. And that's assuming the Trump tax cuts are allowed to expire and the discretionary spending hike of the last two years is allowed to fall back to former levels in 2020. That's called setting a baseline for what comes afterwards.