I'm seeing a resurgence in C. It seems to be coming from several different directions.
The first is from people like Mike Acton:
CppCon 2014: Data Oriented Design
The second is from all the new languages like Go, Rust, Swift. All these new languages need libraries so they all built in good C interoperability so they could be useful immediately without requiring ground up new implementations of everything. So I'm seeing more new pure C libraries being created now than I've seen in a very long time. Library developers know that their libraries will be usable from every language if they write it in pure C.
The third is from IoT. Embedded developers never left C. Now with IoT growing, C lives on.
In all of these cases, they might fly under TIOBE's radar. Most of these people probably don't need to search for C. They already know it and are too busy working on their projects.