You state a compelling alternative hypothesis, but unfortunately you don't present any data that would help us distinguish between the two hypotheses.

Social "contagions"--social pressures inducing particular comparatively novel or previously low-frequency behaviors--do happen. For instance, there are suspiciously few goths these days; goth body modifications are way down.

It's a start, but not enough, to present an alternative hypothesis of derepression. There certainly is derepression. But there's also a lot of positivity and camaraderie which can create pressure.

Because people are complex and different, noting that some people have deep, abiding, intrinsic gender dysphoria is not enough to demonstrate that the only factor is intrinsic. If some people--like, 90% of people or more, by some estimates--can stay closeted, why can't some people also feel pressured to come "out" of a closet they were never really in in the first place? It doesn't seem intrinsically impossible.

So then the question is: it seems possible, but does it happen? How often? Is it worth worrying about?

This isn't the easiest thing to answer; Lisa Littman doesn't do a great job addressing that because of course whole groups of friends might have been friends to begin with because they all had commonalities of discomfiture with their gender, so her observation is of a selection effect not a "contagion". But you also don't make any progress towards answering it.

People don't agree to disagree about whether bats are mammals. This isn't an area that should be left up to disagreement either, and for that, high-quality evidence is needed, not just a perspective that is plausible to some but which hasn't been rigorously tested against other perspectives that seem plausible to others.