A dried mud structure attached to an object could easily travel without anyone noticing it.

By the time someone discovers it, the original location may be impossible to determine.

That means the mysterious object could represent several stages of a story:

An insect built it somewhere.

The nest dried.

The object became detached or remained attached to another surface.

It was transported.

Eventually, someone found it in the aircraft environment.

That explanation would be very different from an insect actually building a nest directly inside an airplane.

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The Shape Is More Interesting Than the Size

The object appears relatively compact, but its shape is unusual.

Instead of being a single solid lump, it looks as though many small pieces have accumulated into a larger structure.

This suggests a construction process involving repeated additions.

That fits well with the way some solitary insects build nests.

A single insect can make one chamber at a time.