It asked you to install flash player because it has flash content on the page that it wants to display. Not really a privacy concern, if you install it from actual adobe site itself. Third party sites are highly discouraged. On the other hand, plenty of people, including myself, would advise you to avoid flash because of it not playing nicely with Mac OS X in general. In my opinion it is a resource hog, and unnecessarily heats up the mac. Sometimes it is a necessary evil, but I just use Chrome in those instances, because of having Flash support baked in. I end up trading one necessary evil for a slightly lesser necessary evil...
p.s. I really wish Chrome was better on Mac