"Why is the logical conclusion that the fungus is controlling the ants?"
"More logical is that an ant knows that it is ill and does not want others to become ill so moves as far away as it can. Then funds a safe place under a leaf."
(Disclaimer: I Am Not A Biologist and the following is speculation)
This is where words like "control" can be misleading (if not anthropomorphic) in such contexts. It's quite likely that this *is* the case and the fungus has evolved to exploit this tendency of ants. It could be said to be "controlling" their brains in this way.
This is, as you say, far more likely than an organism as simple as a fungus somehow being able to manipulate the ants' brains in a more complex manner- exploiting an existing and inherent characteristic of ant behaviour. However, it doesn't actually contradict the headline.
It's quite possible that the story got distorted a couple of steps down the line from the original source (as happens with science stories) and will be "KILLER MUSHROOM DOES BRAIN SURGERY ON ANTS" by the time it appears in The Sun.