You were right.
"Cater" takes both prepositions, the difference being:
when we 'cater for', we provide with food and drink, as in "cater for a buffet dinner".
when we 'cater to', we provide a person with what is needed or required : "The school caters to children with learning difficulties."
we try to satisfy a particular need or demand : "He catered to her every whim."