This is a new one ....

You do have to lift weights. Think what's more likely... that's he's a biological miracle capable of the biologically impossible... or that the machine was inaccurate. There is no machine, by the way, that can truly accurately show fat and muscle percentages, though DEXA can come close. You can also mess up dexa results just by drinking water... so.... hate to be the bearer of bad news, but he most likely didn't.

A lot hangs on what type of device they used. Some medical offices are using bioelectrical impedance devices, functionally similar to the bioelectrical impedance analysis (BIA) scales people have at home. They have a fairly wide error range, and can be distorted by things like hydration levels. Any body composition test has an error range, but different methods have different probable accuracy.

Muscle gain isn't impossible during weight loss, but it's much less likely during loss, much less likely when older, etc. If/when it happens during weight loss, it would be slow. Loosely, we'd expect that the faster the fat loss, the less likely muscle gain, and the slower any muscle mass gain that does happen.

Three pounds muscle gain in a few months? Maybe. How many months? Depending on the number of months, 9 pounds of fat loss could be fast loss (if 2 months) or slow loss (if more like 6 months).

Weight lifting or other obvious resistance training isn't the only way to gain muscle. Any progressively strength-challenging exercise can cause muscle gain, but resistance training generally and weight lifting specifically are going to be faster and more efficient ways to trigger it. I gained muscle rowing, but it was very slow to happen, happened at constant body weight, and I don't have an estimate of how many pounds of muscle were added.

At the end of the day, he's making improvements to his health. Big ones. And that's what matters!

thinking math-ly, if his weight has gone down so considerably, even if muscle mass remained same (assuming acccurate device) that would mean muscle % would have gone up in correlation, right?

I start at 240 with 20lbs muscle (pulling these numbers out of my hind end btw). That’s .0833 % muscle mass.

I lose 60 pounds, remaining at the same 20 lbs muscle. Current weight 180. My current muscle mass is .11.

I haven’t added any muscle, but now muscle is a larger % of my whole?

it’s awesome he’s lost 60. Congratulate him, and encourage him to move more. It’ll certainly be easier now!

Like everyone else, I'm a little dubious about the measurement device accuracy. This is a common issue, not specific to your husband.

Down six pounds in "past few months" suggests a minor calorie deficit. Say that's three months, that's an average deficit of 230 per day. A deficit under about 500 is beneficial to retaining muscle mass while also doing frequent lifting and maintaining high protein (1g per pound lean body mass, or close to 1g per pound bw unless you're obese). A beginner can also make rapid muscle gains from lifting. It is possible to gain muscle in a small deficit, especially as a beginner lifter. Without lifting at all? I'm skeptical. Maybe he has been active enough that most of the weight lost is fat, plus maybe some machine error skews the results. Either way, it sounds like he's on the right track. I would definitely encourage lifting.