To understand what mutual learning is, we can compare it with another term: traditional learning.
Traditional learning is largely one-way communication between an expert (like a teacher) and non-experts (like students). Imagine, an expert teaching you to not make a bonfire on hot, windy days. Maybe you have interesting discussions on the topic, but it is unlikely the expert(s) learn from you.
On the other hand, mutual learning is two-way communication between different people (they can be experts or not). In recognising that all of us has valuable experiences and knowledge, everyone learns from each other. Imagine, fire practitioners and shepherds learning from one another on how to combine prescribed fire with grazing practices, which are both useful tools for wildfire prevention