Huh? I think he's saying OR not AND. Why would two separate pieces of evidence make the whole less probable, that makes no sense, whether you spell out the whole thing more formally or not.
That doesn’t make sense either. Seems like someone is falling prey to an intuitive fallacy of probability.
The weird model is just wrong in the first place. The commenter we’re discussing conflates the probability of two people saying something with the probability that what they say is true. So yes, you have to model the situation correctly in the first place.
On the other hand, if those 10 were engaged in complete groupthink (so no additional information beyond the first guy), the overall estimate would remain 10%.
In general, the answer would lie between 0.1 and ~0.65 depending on how their estimates influence each other.