I'd also hold that the only thing this plaque could ever give is clear sign of artificial creation, and by virtue the (possibly past) existence of some entity capable of creating it. Maybe they'll get a vague idea of what we look like, but if "their" culture does not commonly depict themselves in 2D as we do, or "they" have vastly different morphologies, even that would be unclear. The context needed to understand our attempt at showing our location might also be lost if the thing went far enough.
Maxwell published in 1873. The double slit experiment was 1803, subatomic theory developed throughout the 1800s, and Planck proposed quanta in 1900. The first radio transmission across the Atlantic came approximately 2 years after Planck's theory.
I doubt it is plausible to develop anything resembling industrial technology without stumbling across certain fundamental truths in the process because doing so requires a sufficiently accurate model of physics.
The inventor of the arc converter was 18 at the time radio waves were discovered, 34 at the time he invented the arc converter, but 56 and with only 17 years left till his death when the era of modern quantum mechanics started with the invention of wave mechanics. It's a lifetime apart.
Some discoveries were made during that period that are of course still relevant.
The only way this doesn't work is if the aliens who retrieve the plaque from deep space somehow stabilize in the long term at a point where they've developed rocketry and general space travel but not radio or an understanding of quantum mechanics.
However the above would seem to imply that they don't do radio astronomy, don't have a very good understanding of light (since it's all photons), and don't have high frequency electronic circuits (since designing those requires accounting for RF interference). I guess their understanding of optics is also lacking and their understanding of chemistry is rudimentary and stagnant over the long term.
In other words, aliens permanently stuck at a late 1800s technology level that have nonetheless developed the ability to travel across interstellar distances. And spotted voyager (a very small cold object in deep space). And retrieved it intact.
That's undoubtedly a very cool premise for a scifi story but as far as real life goes I think your time would be better spent worrying that voyager might be eaten by a species of space fairing wale.
RF equipment is not built or designed by people working with or having understanding of quantum mechanics. Understanding waves could come from observing liquids, or if audio exists to them, that. Designing around noise can be done empirically as we do. Quantum mechanics in this area only matter due to our current chip manufacturing process, but who says they use semiconductors?
On the other hand they could also have a better understanding of light and photons and never build RF into their core technology stack, thereby not having people observe and analyze the hydrogen line.
The only strict order is that we know now that our previous theories were complete garbage, and we are still waiting to discover why our current theory is complete garbage.