Whoever told you that was wrong. It isn't a given that he will be sick, too. He may "have" it, but at any given time about 40% of the general population has strep in their system. It's very very common and almost impossible to keep totally away from it. But, not everyone who has strep gets sick. The body does a pretty good job of fighting it off, obviously, or else we'd be sick with strep throat (and worse) *all* the time. I think boosting his immune system and getting extra rest is a good move in a case like this, and probably good idea anyway, of course.
And if he gets a sore throat, take him in right away for a culture test and treat it if need be. Don't believe all the hype about not having to worry about strep infections in young children. That is also not true.