There was one in-vivo study of minoxidil inhibiting collagen synthesis, so that's covered.
I don't know about how it relates to the smoking effects. I think it has to do with the normal distribution of minoxidil sulfotransferase. If you're familiar with enzymes that can be found with varying concentration in humans, you will know they follow some Gaussian distribution. Much the same way that people who minoxidil doesn't work for at all are at the lower end of this distribution, the people who suffer from side effects have so much minoxidil converted to minoxidil sulfate because they are on the upper end of this distribution. Because of the high conversion rate as a consequence of the local concentration of minoxidil sulfotransferase, the tissue where minoxidil was applied gets saturated and minoxidil sulfate starts spreading. The officially listed side effect of facial bloating due to water retention is proof of minoxidil sulfate spreading beyond the tissue where the minoxidil was applied. If you're on the upper end of the minoxidil sulfotransferase distribution, the amount spreading will be even more, to reach concentrations high enough to inhibit collagen formation. Just my theory though, but I think it makes sense.