Humans began to rapidly accumulate technological knowledge 600k years ago

You have to think that there were breakthroughs in communication technology — not just language in general but possibly also one individual who happened to be good at explaining things, either before or after language, who both taught more people, but also taught them how to teach — that led to step changes in technology.

It all starts with imitation of some sufficient fidelity and generality that seeds a runaway evolutionary process. Language evolved to improve the fidelity of imitation much like how genes evolved pathways to minimize random mutations during copying.

Once imitation gets good enough (general and accurate) were capable of spreading behaviors (phenotypes) without having to wait for folks to be born and grow up.

That's culture, and it's known to exist among animals in a limited way.

We don't really know what the upper bound for non humans is, because we don't know exactly what's being communicated by, for example, whale song.

I wonder whether we (as human) are merely the first species that managed to overcome initial barriers to developing culture and tech and thereby preventing any other species to do the same (for now).

It feels like bipedalism, opposable thumbs and strong social behaviour and other factores were the perfect storm at the perfect time.