What does it mean when we say that in blockchain, consensus determines the truth?
The system of compute nodes all verify a claim. Through mulitple independant, non-bias responses a sum of true -vs- false votes will agree on the validity of something. Being that this is computated without human influence the mathmatical detrmination is trusted because the majorty have all determined an output that do not conflict.
How is this different from how truth is determined in a central database?
Truth in a centralized database is established by the admin. In some cases the argument can be made that a baseline of observed results is used as that “truth,” but, due to a limited set of computers in that pool, and a possible corrupt dataset the “truth” is ultimately what the admin says it is.