One possibility is that he simply tricked you, unfortunately.
It is possible if you don't see it on the Pokemon summary screen. It could also be a glitch but that's more unlikely.
>When infected, a Pokémon's status screen will indicate it much as it does any other status condition.
The icon you should see in gen 6 and in gen 5 is
Make sure you check that and make sure you talk to a nurse in a Pokecenter. They comment on the Pokerus if you have it.
What they say in generation 6:
>"Oh... It looks like your Pokémon may be infected with the Pokérus.
Little is known about the Pokérus, except that it is a microscopic life-form that attaches to Pokémon.
While infected, Pokémon are said to grow exceptionally well."
If none of that happens they he tricked you. Sorry. :/
Hope I helped.