It is impossible for the stock market to be irrational, but individual actors within are often irrational.

Within the game, "the stock market," it is rational. The game is "What do I think other people will pay for this?"

The price of a given stock is always rational under that game.

Your problem is assuming the price is justified based on any particular aspect of any company in question. The answer is almost never "Yes." The price doesn't represent competence, it reflects confidence.

The market is a confidence game, and so the prices are always rational. The game itself is even rational! However, the actors are not always or often rational, and prices are only ever coincidentally (and rarely) aligned with the actual value.

The price going up that much in that short of a time period is very rational, because the price is a function of what others think others are willing to pay for it, rather than trying to reflect anything wider.