Contact Form 7 by default displays the message, “There was an error trying to send your message.” in cases where email sending has failed for any reason, and uses the same message in cases where spam activity has been detected. You might wonder why it doesn’t say something different like “Form submission aborted because we know you are a spammer!” or something in spam cases.
Not telling the submitter the fact that you’ve detected spam attempts in their submission is a kind of worldly wisdom. If the spam detection was true, and the submitter was a real spammer, you shouldn’t give them extra information that you know that. On the other hand, if the spam detection was a false alarm, you wouldn’t want to make them angry by calling them a spammer. In either case, it is wise to not share the reason.