Hey Voodoo,
The books says the argument is causal because, well, it is causal
Before addressing why that is the case, let me first note that indicator words aren't necessary to indicate the presence of causality. There are numerous ways to get across an idea such as causality (or conditionality), and the lists of indicator words we provide cover the words most often used by the test makers. But, I also stress in the books that you have to really understand the core idea because there won't always be indicator words present. This same concept applies all over the test. For example, conclusions. They often come with indicator words, but not always. Indicator words are a great start and get you a lot of knowledge and understanding quickly. But you need to know the concept well also.
That said, in this argument, consider the conclusion (which is conveniently prefaced by the conclusion indicator "clearly"
). It basically says that modern navigation systems are being put at risk by the electronic devices carried by passengers. Think about that for a second, especially in the context of the premise about problems that occurred when a passenger turned on a laptop. The words and statements of the author clearly indicate that there is a belief that these electronic devices affect the circuitry, which in turn creates greater risk. That chain of events is causal.
You ask how electronic devices can cause something. I'm sure you understand that concept in general, but the idea here is that, for example, a passenger turns on a laptop, which produces various electronic signals. These signals then disrupt the circuitry or signals of the aircraft electronics, causing problems like dials dimming and navigation problems (this is a real-world problem by the way; it's why they make you turn your electronics off when a plane takes off and lands).
Please let me know if that helps. Thanks!