"Nigerians have abandoned cash..." ------ Cash is King in Nigeria. At least 70% of consumer transactions are still in cash. The Central Bank issued a cashless policy some years back, encouraging an explosion in mobile wallets, alternate formal financial institutions, etc, but they have struggled. Cash is still king.
"...because they have so little trust in government-issued currency." ---------- Yes, the currency is weak. Against USD, against GBP, EUR, etc. But this has nothing to do with the everyday man's decision to stuff his mattress with cash vs bank with a formal institutions and have digital currency.
In the same vein, the chart in the article, that shows currency as percentage of GDP... This has nothing to do with the relative volume of cash transactions. It's important to differentiate cash vs currency.
"Instead of using banks, they tend to transact in mobile airtime minutes." ---------- This has been attempted once, but i don't know anyone in Nigeria that accepts airtime minutes over cash. Not to be funny, but I've been asking all day, in case there is some movement I might have missed.
Some rural villages even create their own credit instruments, enforced by local deities. ———— From the cited source, the paper focused on "a limited number of local communities of the Igbo of southeastern Nigeria”. We are talking about a few hundred people, that turned their local 'church' (oracle/deity) into a lender, sourcing funds from the large wealth they have received from donations over time. And yes, they give out these loans In CASH.