The first successful asteroid mining startups became multi-trillion dollar corporations overnight, not just because of the vast quantities of rare-Earth materials they extracted, but because of the novel applications such an abundance of these useful materials had. Materials science leapt ahead by decades, maybe even centuries - newer, ever-higher temperature superconductors made fusion not only viable, but reliable; cheap, even.
Fusion, in turn, allowed us to achieve the holy grail of 21st century propulsion technology: the torch drive. Powerful and efficient. We could now fly freely about our home system, making asteroid mining even easier -- and as we always do, we began to look further afield.
Fusion drives, a staple of early 21st century sci-fi, ultimately proved to be just as effective - and in some cases as dangerous - as portrayed. They work on the same underlying principles as a conventional chemical or ion drive, ejecting mass out of the back of the ship to achieve forward acceleration, following Newton's third law. Whereas chemical drives produce a large amount of thrust with low fuel efficiency and ion drives produce a small amount of thrust at high efficiency, fusion torch drives are both powerful and efficient; they need comparatively little reaction mass, as they can accelerate it to much higher velocities to achieve the same effect.
Dragonfriend's kind adopted fusion drives long before humans had even evolved, though they're still recognisable in both form and function. A skilled human engineer would be able to make high level sense of one, but not be able to fabricate spare parts - or replicate their sheer performance.
Whilst human torch drives burn a brilliant blue, those of Dragonfriend's kind are almost invisible to the human eye, emitting light mostly in the high UV band, owing mostly to their exhaust temperature; however, they emit less energy as heat and photons in total than their human counterparts, instead imparting far more of their output as kinetic energy in their reaction mass. These drives sit at - and push - the theoretical limit for even the most optimistic fusion drive designs we have today, and could be surpassed only by antimatter propulsion in terms of fuel efficiency.
Similarly, their FTL drives operate on many of the same principles as human warp drives, though they have been redesigned and optimised to the point of being almost unrecognisable to any human engineer, taking advantage of effects both quantum and as of yet unknown to human science to achieve effective velocities in excess of 50kc.
They never trialled Interspace drives after only a handful of abortive attempts - the extreme high energy radiation environment and imprecision were deemed to be unacceptable risks to a species that, at the time, suffered from dwindling numbers and a gamut of existing radiation-related conditions. By the time they found themselves on their feet, warp drives had progressed enough to make travel times effectively meaningless. Only humans were batshit insane enough to scale Interspace technology up... or rather, were they lucky?
Antimatter propulsion also never saw use due to reasons of safety - the inherent risk of antimatter fuel breaching containment was - and still is - deemed too much of a risk for the marginal gain it would provide.