Other mistake: When J is falling from the Chrysler building, the soles of his CGI shoes are completely black, brand new and spotless, which is impossible unless he got up there flying or changed his shoes in mid-air. (00:36:00)
Other mistake: J exits the Flatiron building and a woman in a yellow dress starts walking behind him. He looks at the street ahead and the same woman is walking from right to left. (00:38:35)
Other mistake: At the diner, J is given a strawberry rhubarb. For the first few seconds after being given his plate, he is never shown putting his fork in his food, yet he still chews anyway. (01:03:50)
Chosen answer: He saw J's father murdered by Boris. In the unaltered timeline, J says that his father wasn't around. We see this at the end and it's also why J was recruited into the Men In Black. K was keeping an eye on him the whole time.
Brad ★