He said it correctly: it wouldn't meet the legal standard. That should mean, correctly, you cannot invade people's privacy, but again it's pretty unrelated to "are they investigating crimes or not."
Edit: GP's comment was edited from "That is to say, they're not even investigating a crime." That claim is untrue.
> That isn't true. It means it wouldn't reach probable cause.
So, investigating a crime should lead you to some evidence that you would than have a substantial reason to request a warrant to target an individual. You're letting the tail wag the dog if they can do the targeting before they know who to target. If they don't have any evidence to target a person but they suspect that person of doing something illegal then that's called a hunch. Scooby doo and his gang were great at following hunches, but that shouldn't be how the FBI operates.
The reason for allowing them to spy on foreigners isn't because foreigners are criminals. It's because we believe surveillance of foreigners might provide some protection for us. They are trying to prevent crimes, not solve them.