Scientists have excellent language to describe these sorts of things (ambiguity and confidence in guess). For example, from the actual paper's abstract:

"""Quantitative analysis of the radar signals shows that this bright feature has high relative dielectric permittivity (>15), matching that of water-bearing materials. We interpret this feature as a stable body of liquid water on Mars."""

It's absolutely true that we can't call this a strong positive siting, it's more of a "good evidence which is not completely unambiguous".