As an adult with a vaping habit, I can see how that happens. If you're a kid, and thus have unstable access to nicotine vapes (because they're illegal for you to buy), you'll be highly motivated to get your nicotine fix from something if your source of vape liquid dries up. Since cigarettes are more common, the result is a kid being likely to smoke sometimes.

Same thing happens to me (albeit far, far less frequently) when I'm out at the bars with my friends until 2am when I discover I'm out of juice. Since vape shops tend to keep normal retail hours, I'm limited on getting my fix from whatever the 7/11 is selling. If that's Marlboro reds, I'm probably going to smoke a cigarette or two.

Key difference between it being a "gateway drug" and not is the fact that I'll end up throwing away that pack the next day when I can refill my vape. Because smoking sucks in comparison. Not only on health grounds (not a huge concern for most nicotine addicts), but on basic grounds like "making you smell like shit", "hurting your throat", "tasting bad", and "not having the oppurtunity to be used nearly as frequently".