As I recall it, Munger's moves at DJCO were somewhat known through the quarterly filings for DJCO. The wording in the early filings was vague, and didn't identify what was being bought, but based on the public comments of Munger and Buffett, alert investors who followed the pair could guess that Wells Fargo was the likely target. From memory, confirmation that it was Wells Fargo (and possibly one or two other positions) didn't happen until much later.
So, "in the know" investors could surmise what was going on. However, that time in the market was so volatile and gut-wrenching that even those who knew, may not have wanted to act on that knowledge. While I knew Buffett and Munger were happy to buy as much Wells Fargo as they could as it slipped under $10, I didn't do the same (for a variety of reasons). It is hard to overstate the emotional impact of what happened in the second half of 2008. There were days I felt sick to my stomach and worried about the possibility of an implosion of the US financial system. The hardest thing to do was to sell something good that was down 50% to buy something else that was even cheaper.
With all that said, the idea of portfolio cloning, or riding coat tails isn't new. Sites like Dataroma (http://www.dataroma.com/m/home.php) are useful for tracking this sort of thing. To me it's useful to see who's buying what as a source of ideas, but wouldn't suggest anyone buy just because someone else is buying.