Interesting how the finger pointing started before any investigation was done.
We do not know if it was caused directly by multipool. The timing just seemed to perfect for it not to be.
It is not any easy decision choosing the chain to be considered valid. Since the only exchanges to currently trade the coin are on the same chain as you we are going with the longer chain.
A pool mining a coin cannot cause a hardfork. The fact that you are even considering a pool as a possible reason for the hardfork, as someone else said, is incredibly irresponsible and suggests incompetence as a dev. Especially when the pool in question had all of your recommended addnodes in the config since day 1.
A hardfork is caused by a segmented network where blocks on both chains become fully confirmed. This means that whatever pools were on the other chain were disconnected from the main network long enough to mine and fully confirm blocks.
What I suspect happened is that Vern's pool or another pool did not have the right addnodes, but was operating fine for a while because it was well connected. Most likely, their coin daemon was restarted at some point last night, and did not fully reconnect to all the nodes or connected to a different set of nodes that was already forked. Then they continued to mine and fully confirm at least 1 block (which requires 25 confirms) before the two networks reconnected to each other. Multipool and the other pools/solo miners on the main chain had also mined 25 or more blocks.