Whether to be concerned about this sign is a matter of how strongly and how often you see the sign. Also, consider how you might feel were you your child. Maybe people actually are not to be trusted and are out to get him. Your child may be right.
It is not unusual for your child to feel used sometimes and to be somewhat leery of people. It becomes a problem when he starts changing what he does or does not do, where he will and will not go. It is a problem when it interferes with his normal, day-to- day activities. The problem gets worse when your youngster thinks people are trying to hurt him and more so if he is not sure who "they" are or if "they" are not people who are likely to hurt him. For example, he might come to believe most teachers or perhaps you are trying to control his mind or find a chance to kill him.
Are your child's fears far beyond anything real, beyond reason, or quite weird? If so, he likely has a very serious mental illness-related problem and needs psychiatric help.