Under US law (other countries may be different), it is clearly not insider trading. A Boeing customer has no duty of confidentiality to Boeing and they didn't misappropriate the information from someone who did, so they are not an insider.
Even though they have access to information that the rest of the public doesn't, it is still perfectly legal to trade on that information.
Even though they have access to information that the rest of the public doesn't, it is still perfectly legal to trade on that information.