[AlotOfReading]

When we start getting into hypotheticals, it's useful to reframe the discussion in more concrete terms. What would it mean to have a "small industrial society"? I can think of a number of "things" that would fit that term:

1) Ancient Aliens: Essentially similar to what a human martian colony would look like. In this case, resources, population, and knowledge are brought from off-world and there's little to no local exploitation. The only way to detect something like this is direct material evidence, which also means it's practically unverifiable. Not really a useful hypothesis.

2) the dystopia: an anomalously advanced human society surrounded by hunter-gatherers in the wastelands outside. As a twist, the population is small and in-line with contemporaneous HG populations. One problem with this scenario is that it just doesn't look like any human society ever discovered. There's libraries worth of work on how technological development happens and the two big accelerators we see across most of history are high (effective) populations and communication "density". The lower either of these are, the more likely that the information network breaks down over time. At the population levels we're talking, simply having enough people to do all the various jobs that need doing in a high-tech society is a problem, let alone redundancy and exploration of new ones.

3) Non-human societies: Something incredibly old, non-human, and lost in the mists of time. This is where you get into the silurian hypothesis and given enough technology/magic/moved goalposts, it gets difficult to say anything concrete. There would probably still be evidence in some form or fashion, but ultimately you have to define some model of what the society looks like it to actually say anything about it.