Yep. Imho this doesn't pass Occam's razor.

Finding: "Objects with chemical composition that's unknown on Earth".

Conclusion: "Likely originated from outside our solar system".

Simpler explanations:

"Formed on Earth through previously unknown process".

"Formed elsewhere inside our solar system".

How many extraterrestrial (but inside solar system) substances do we really know? How much extraterrestrial substances have been sampled, from how many locations on how many objects, exactly? And even on Earth, do we know all processes through which materials are formed?

Yes, extrasolar origin is one possibility. The most likely one? Hmm..