A public company does not have an obligation to disclose acquisition, merger, buyout "talks". It is just "talk".
Yes they are required to disclose material information, but "talk" is not material until it progresses to something more concrete that will have material affect on the valuation of the company stock.
I remember that last trading halt, and then the company came out and said they were not aware of any corporate development that would justify the price increase. These rumors can really make people jump sometimes.