The exact meaning is that, of the several facts that reasonably support the conclusion of Loum's being the Chinese merchant, this is the most significant. The sentence as written does not specify whether that conclusion is true or false. That failure to specify may be deliberate or unintentional, but, as quoted, the sentence does not speak about truth, merely about plausibility.
If the intended meaning of the sentence is that the identification is valid and that this fact is the most significant clue to that validity, then the sentence is not well drafted. It might be revised to say:
That Loum is the Chinese merchant is indicated by several clues, of which X is the most significant.
If the intended meaning is that the identification is not valid despite the clues, then the sentence is very badly drafted. It might be revised to say:
Several clues, of which X is the most important, seem to lead logically to the misleading conclusion that Loum is the Chinese merchant.
If, however, the intended meaning is to leave ambiguous whether the plausible conclusion is also valid, the sentence is perfect.