The phrase "film is very visual" means that movies and TV shows rely heavily on images, actions, and visual effects to convey meaning and tell stories. In other words, much of the information in films is communicated through what we see (e.g., facial expressions, body language, scenery) rather than through spoken language alone.
So, while watching films can help with understanding spoken English, it's possible to follow the plot and understand much of what’s happening even if you don’t fully understand the dialogue. Because film is so reliant on visuals, learners might not always be practicing listening or language skills as much as they think when watching TV or movies.