Yes but this looks more like habit disruption more than "biologically gaining weight somehow". People that lift often eat more. But mostly protein, and stimula

Yes but this looks more like habit disruption more than "biologically gaining weight somehow". People that lift often eat more. But mostly protein, and stimulating muscle every day makes sure it will get developed and consume more calories to maintain itself. If you stop lifting altogether, not only muscle mass stops growing but also starts to shrink. If you eat the same, you will gain weight faster and with less food than before.