Confusing fork with activation date example

[Giszmo]

Early proposals such as BIP16 Pay to Script Hash (P2SH) used a predetermined Flag Day to activate on the network. P2SH was activated on April 1, 2012 at block 173,805. Following the activation there were reports that some Miners who failed to update from 0.6.0 rc1 were stuck at block 170,060.

How were Miners stuck on an earlier block for lack of updating? Did the updated miners fork on the earlier block? Also it should read "nodes" and not "Miners" as problems syncing the blockchain isn't exclusive to miners.

I did not read all the linked information but it doesn't look like a normal thing that would happen with this kind of fork activation. Especially Gavin's closing remark "If there are any Berkeley DB database experts reading this we could use your help figuring out what the heck is going on..." looks like this is not the most informative link for this issue.