Yeah, this is similar to the Baghdad battery: https://en.wikipedia.org/wiki/Baghdad_Battery
No proof whatsoever that it was used for generating electricity and making anything useful out of it.
Sure we have no proof of the opposite either, but when something leaves no historical trace and is an alleged lost knowledge that would have been completely forgotten for centuries before being rediscovered again, the probability is very low. Once we figured out how to master fire and the knowledge propagated, we never forgot how to do that, not for a single year that I have heard of in the history of mankind. For instance. Same for pretty much all great discoveries.
Now one could maybe argue that some discoveries didn't find any sufficiently remarkable use for them to stick, and may have been forgotten for a long time due to their lack of usefulness at the time. Maybe. Can we consider them real discoveries in that case? Were people at the time even aware that it was something worth considering a discovery at all?
While I agree that the chances of this being a real and intentional battery, there is evidence for lost technologies. One of the most prominent - Greek Fire. Roman cement was lost for centuries. And as I understand it, the technique for applying a bed of minute gold particles to jewelry in Classical times is still not possible to replicate.
Why good stuff gets lost is complicated. Your fire example is a cheat in a way. A simple technology, nearly universally useful and producible with materials available nearly everywhere.
Greek fire was a military secret, so death of a small number of people could explain the loss, or perhaps it was dependent on a unique source. I know of one widely used technology which works best with material from a specific mine. The reason is not well understood. The Roman cement depended on a relatively unique source and a relatively large industrial base. When that critical mass went away the material wasn't practical so loss of the knowledge is not surprising. Our semiconductor technology is vulnerable to the same thing. While the general knowledge of the subject will survive for a while easily, the huge body of expertise necessary to make it work - everything from crystal growth, to clean rooms, mask making and the lot could evaporate overnight. The jewelry thing is the kind of craft knowledge hoarded as a trade secret. Again vulnerable to a relatively small number of people dying and small numbers of documents being lost or destroyed. Combine that with a reduced market in collapsed societies and much stuff could go away.