The expat Turkish site Ahval offers the following commentary:
Erdogan’s theories on the relationship between inflation and interest rates may come partly from his experience in business. Before entering politics as mayor of Istanbul in 1994, Erdogan used to run a food company.
Turkish CEOs tend to borrow heavily to cover their operating expenses. When interest rates are rising, it creates uncertainty and higher costs, which companies then pass on to their customers in the form of price hikes. When interest rates are falling, firms are more willing to reduce prices because their own expenses are declining and their financial outlook becomes rosier.
We don't know if Erdogan really thinks this way, but at least it is an alternative explanation to pure Islamic commitment to low interests. The source also claims:
While few economists agree with Erdoğan’s stance on rates, neo-Fisherites – who use arguments put forward by Yale University economist Irving Fischer – advocate real interest rates as a tool to control inflation. The theory goes that if a central bank brings down nominal interest rates and keeps them there, then inflation will inevitably move down toward that level. Should a bank raise nominal rates and keep them high, then eventually inflation will accelerate.
A quick google search finds that "neo-Fischersim" really exists and does advocate just that, although it seems to have few (in any) actual academics behind. It's unclear if Erdogan has even heard of it though... (There is even an article in The Economist [linked from the previous source], which debunks neo-Fischersim.)
Erdogan's economic thinking aside, since Turkey had eneterd a recession in the last two quarters of last year, which eventually brought down inflation in the first half of this year, even Financial Times agreed that their central bank should have cut interest rates at some point.