That is the MAX observed IO so it might be that there was sort of Caching somewhere that caused it.
It is but what we do with the 5min collection is to take the max value and avg. What you are seeing is the avg 5min interval. At some point it was at that max you are seeing.
I would open a VM ware support call and here what they have to say in fixing it for you.
Haven't opened a case yet but maybe someone has had to deal with this. I may open a support case tomorrow for it if no one has any ideas.