Citing deaths as a percentage of tests is just a way to find a positive statistic to skew the narrative. It has way more variables than you're giving credit for and probably means less than you think. All it tells us here is that our hospitals are probably doing a good enough job where they can, which is certainly a good thing, but doesn't tell us much about the outlook of the virus in our country moving forward.
At the end of the day, we're still too high in deaths per million and are only recently catching up in tests per million. And we're clearly too high in cases per million, even while being behind some major countries in our testing rate. We aren't close to herd immunity and we're not even sure yet about the reinfection potential. These things could be easily communicated to a mass audience, Trump has just only been interested in picking&choosing what he thinks will make him look good, and most of they country seems to be catching on to that.
I don't know how much this specific interview will hurt him, but there's a reason he spent so long shying away from non-Fox News interviews. He looks like an idiot any time he's challenged on anything, much worse than Joe Biden and I don't think highly of Biden at all. And we're likely to get more of that as the campaign season heats up. We saw this in 2016 too, but Trump's mental acuity seems to have only gotten worse from then to now.
I'd bet most hardcore Trump supporters won't jump off the boat from these interviews, they seem to always find justifications and excuses and will just support him no matter what. The problem is Trump is already behind, and these kinds of events won't help him catch up.