your comments are either behavior based or strong indicators of decision making skills and results. And, you were with him sufficient time to observe a number of these. I find that behavior and decision making skills of an adult are set and do not change...thus such first opinions are true even after more time spent with the person. I, too, form opinions based on behavior and am about 95% accurate, given a first interaction which is of reasonable duration and in a "normal" environment. A meeting at a party or casual meeting may not provide a sufficient sample size to achieve an opinion of reasonable accuracy.
Now, if you form an opinion based on attractiveness, gender, race, religious affiliation or any other such criteria, then your opinion, likewise, will remain fixed even though you get to know the person for longer. These characteristics, if used, hook into a person's own existing biases and beliefs which will only infrequently fully match the actual individual's behavior and life decisions. Seems to me that this dichotomy can, unfortunately, foster a level of rancor, conflict and anxiety between individuals .