Niskanen blasted in an excellent volley to give the Grecians the lead shortly before half-time at St James Park.
It paved the way for Exeter’s second league win three games – with both those home victories coming with a clean sheet.
Caldwell said Niskanen’s goal was reward for the way he conducts himself at the League One side.
“He was 45 minutes walking into this stadium, speaking to every supporter, signing every supporter’s calendars and pictures because he loves this football club,” he added.
“What he gives to this football club on and off the pitch deserves goals, but football can be cruel at times and yet he’ll be the first to admit he has to score more.
“If he can score left-footed volleys outside the width of the goal, then I’m a happy man and long may that continue.
“But his assist for the third goal as well was brilliant, not just to kick it anywhere, to know that we could cut back into that zone that we identified could be dangerous
“I can’t speak highly enough of Ilmari, it’s thoroughly deserved and long may it continue.”