> _My manager took my interview, so he could have always told me about the short contract._

Correct. There is a reason why it was not disclosed , most likely, you are not to be bothered about the stint of the current project.

While I do not disagree that you should have been given a fair heads up, however, this sounds very unlikely that a new hire was hired only for a 3-month requirement. It may be possible that either

- they have possibility for further extension
- they have other work / projects lined up after the current one is delivered.

As of now, I do not see anything to get worried. However, you can have a word with your manager regarding the road-map for the current project which should give you the idea about the status.