Answer:
False impression.
Step-by-step explanation:
An impression is one of the crucial factors that determine how another person perceives, thinks, or forms an opinion about a person or thing without giving a conscious thought or based on very little evidence about it. Therefore, impressions often lack authenticity due to ignorance of conscious thought and sufficient evidence.
In the given description, the initial impression of thinking about the other person present in the class as 'rude' would be categorized as 'false impression' as he formed an opinion of him without paying attention to appropriate evidence or consciously analyzing his behavior which is later reflected to him with his friendly and present behavior('says hello, smiles, and engages you in conversation'). Therefore, the initial impression would be categorized as a 'false impression'.