In the IEnumerable<string> keys overload of HybridCache.RemoveAsync, the single-key case calls through to HybridCache.RemoveByTagAsync(string tag, ...) instead of to HybridCache.RemoveAsync(string key, ...).

This looks like a simple copy/paste error of the IEnumerable<string> tags overload of HybridCache.RemoveByTagAsync, which otherwise looks basically identical.