I think what he(?) was pointing out simply that the lack of design intention doesn't mean lack of functional capability. Certainly my fingers weren't designed to type, yet there it goes. The other side of such a fallacy would be akin to stating that because I can type with my fingers, they must have been "designed" (intelligently?) to type. So abstractly, I have to agree (since it was posed in an abstract variable replaceable way).
In this case, however, since the scientists know what they'd need to "prove" life, they can state that Curiosity doesn't have enough sensor capability to gather such evidence. Rather than stating that Curiosity was not designed to detect life, it would be more appropriate to state that Curiosity is incapable of providing rigorous proof of life.
Now, back to the evidence. Stating that what Curiosity has found is not evidence, may be taken at face value only if we narrow the definition of "whatever Curiosity has found" to the information capable of being gathered and returned, as opposed to the sources of the exhibits under observation (which may or may not have a biological origin, or may or may not be a precursor to biologic functions). A thin metaphysical/epistemological distinction to be sure, but one that is relevant because when we need to trust our senses, we need to know our sensor limits, and when we need to trust remote sensors, extra-terrestrial remoteness is as remote as it gets, and its hard limits cannot be easily overcome once deployed.
In this case, however, since the scientists know what they'd need to "prove" life, they can state that Curiosity doesn't have enough sensor capability to gather such evidence. Rather than stating that Curiosity was not designed to detect life, it would be more appropriate to state that Curiosity is incapable of providing rigorous proof of life.
Now, back to the evidence. Stating that what Curiosity has found is not evidence, may be taken at face value only if we narrow the definition of "whatever Curiosity has found" to the information capable of being gathered and returned, as opposed to the sources of the exhibits under observation (which may or may not have a biological origin, or may or may not be a precursor to biologic functions). A thin metaphysical/epistemological distinction to be sure, but one that is relevant because when we need to trust our senses, we need to know our sensor limits, and when we need to trust remote sensors, extra-terrestrial remoteness is as remote as it gets, and its hard limits cannot be easily overcome once deployed.