Well, I'm impressed they actually did test JUST the vape liquid, even though they're still calling them e-cigs.

Quoting from the journal itself:

There were no significant differences in changes of BAL inflammatory cell counts or cytokines between baseline and follow-up, comparing the control and e-cig groups. However, in the intervention but not the control group, change in urinary PG as a marker of e-cig use and inhalation was significantly correlated with change in cell counts (cell concentrations, macrophages, and lymphocytes) and cytokines (IL8, IL13, and TNFα), although the absolute magnitude of changes was small. There were no significant changes in mRNA or miRNA gene expression. Although limited by study size and duration, this is the first experimental demonstration of an impact of e-cig use on inflammation in the human lung among never-smokers.

The way I read this, it seems like there's a small correlation with inflammation, but there's no measurable risk of developing lung cancer from it (they were doing cancer research after all). Personally for an adult, I feel like "inflammation" is kind of a nothingburger, just stop vaping for a while and you'll be fine. But for kids developing habits, I can understand the concern.

twice a day for just a month

It's empirical, but I've been vaping steadily all day every day since I switched from my 2 pack a day newport habit around 2013ish, give or take a year. Last time I went to the doctor he said I had the healthiest lungs he'd seen in a while.

I was as surprised as you are, frankly. Mostly because of the ports in the past but I guess it's been long enough since then to heal up my surfboard lung. I mean I did notice marked improvement in my ability to breathe about a month or two into the switch, and my ability to smell things came back shortly thereafter, and then the doc visit was years after that, so maybe I shouldn't have been surprised but I digress. In any case 2x daily for a month is pussy numbers, gotta bump those up, try 200 times a day for 10yr and your doc will say your lungs look great if they're anything like mine.