From the above explanation I can understand arbitrage is the purpose of buying bitcoin on the loss but they can sell it to more better price which can cover the actual loss and transaction fee.This trick can be used on many countries where centralized exchanges doesn't have direct buying option for bitcoin with fiat.
The arbitrary aspect was well understood from your statement but it seems the buying at loss aspect is still been misunderstood as I read through the replies above. The price highlighted by the OP isn't a loss price, that's what the particular individuals is willing the sell his bitcoin on that peer2peer exchange and it's even a steal. The Naira rate per dollar for the cryptocurrencies market is totally different from that of the general market. That's just how it works in the country. Nobody can tell you this is the official buying or selling price of bitcoin when converting to Naira.
That's why we make our trades in dollars then negotiate what the price in Naira would be. There's no two exchange selling at exact same price, it varies. Not even the banks or payment options like Master and Visa buys and sells the naira at the official price displayed when you Google. So basically, the buyers isn't buying at loss because if he decides to sell, he most definitely would be making profit immediately.