What determines the order of my contacts on the frequent contact toolbar? I am seeing a contact in recently contacted friends in whatsapp to whom I have not sent a message for a week now. All the other contacts are chronologically arranged except for him. Why is this happening? Is it that he is spying on me and my phone is sending him my history automatically? Or is it normal to be so?
I think from reading the source code here and this line and also from reading the code in the Contacts application that the "Frequently Contacted" list in the Contacts application orders the contacts by the number of times that you've called them. That's the DataUsageStatColumns.USAGE_TYPE_INT_CALL bit. This is also assuming you're using the default Contacts application but since you didn't specify I assumed you were.

So it must be that you've called this particular friend more than any others. To test this try and make a large number of calls to the next person in the list and see if it overtakes the top person.

It could also be the case that you've 'starred' him. If you go on his contact profile at the top there's a star. If this is white then it means that you've favourited him which means he will always appear at the top of the "Frequently Contacted" screen. Just uncheck the star and he'll go away.

There is also the option to clear the list if you like, just click on the Action Menu or your menu button and select "Clear frequents".