by 'blockchain-based' they mean, a normal election happened with traditional voting, and then some of the vote counters uploaded the tally of the votes they counted to a private blockchain
During the process, initial votes that are recorded on ballot papers are to be counted by neutral observers. The procedure, being watched by Agora, is the key step to entering that data on to the blockchain."
https://www.bitguru.co.uk/sierra-leone-presidential-election...
You'll note that they carefully failed to disabuse anyone of the notion that the entire thing took place online.