The red exclamation point shows that there is something special about that Pokemon.
Possible things about that Baltoy:
- It had a far higher level than it should have had
- It had a rare move.
- It had a hidden ability.
- It had perfect IV's in one or more stats.
Encountering more of a type of Pokemon allows you to see more specific data about that Pokemon, such as its actual ability, its held item, its moves, or the number of perfect IVs it has.
(In the full data screen, red exclamation points next to a piece of data signify that that piece of data is special.)