being friendly with a boy you aren’t romantically/physically attracted to and him developing feelings for you isn’t your fault, nor does it mean you were “leading him on”. you are under no obligation to date him.
Even if he gets really mad about it. Remember that it’s his problem that he caught feelings. Not your problem.
Also, if someone is only being nice so you would get in a relationship with them, they are not a nice person.
You are not obligated to be with them for being nice.