> "Our central thesis is that molecules with high MA [Molecular Assambly Index] are very unlikely to form abiotically, and the probability of abiotic formation goes down as MA increases, and hence experimental determination of MA is a good candidate for a life detection system. If our hypothesis is correct, then life detection experiments based on MA can indicate the presence of living systems, irrespective of their elemental composition, assuming those living systems are based on molecules."
You could get a false positive from a pre-biotic but molecularly complex planet, such as Earth in the 100 million years before the origin of the first self-replicating genetic-information-containing entity. Such an environment would contain many complex molecules, whose sites of formation/sources could include metal-rich hydrothermal vents, metal-rich clays, meteorite inputs, ocean surface photochemistry, etc.
In a planet with established life, particularly one with oxygenic photosynthesis , these processes don't allow organic molecules, amino acids etc., to accumulate in high amounts because every system is full of microbial scavengers that take up almost every complex molecule they come across, with a few exceptions (the 'persistent organic fraction' derived from tree lignin etc.). Also, free molecular oxygen is a kind of bleach that eventually degrades many organic molecules.
However, in an abiotic system these complex molecules could persist for hundreds or thousands of years, particulary in the absence of free oxygen. Such a complex molecular soup would then provide many opportunities for the generation of simple living systems.
Incidentally, the most plausible current theory of the origin of life puts the protein-producing rRNA-based ribosome at the center, and the concept is that abiotically produced amino and nucleic acids formed conglomerates, and these bodies developed the ability to replicate themselves by pairing up with free abiotically produced amino and nucleic monomers and catalyzing bond formation (May 2022):
https://www.nature.com/articles/d41586-022-01303-z
> "Structure that links amino acids suggests that early organisms could have been based on an RNA–protein mix."