We're not told the circumstances.
The fact that no players seem to have entered the box as the ball was played, as would normally happen with a penalty, suggests that the penalty might have been taken when full-time had been reached but the referee (in accordance with the rules) permitted a penalty to be taken before ending the match.
If so, it's definitely NOT a goal, since the ball must cross the line DIRECTLY as a result of the kick. If, after being parried by the goal keeper (or after being deflected by a post) the wind or the spin on the ball then causes it to change course and cross the line, no goal can be awarded because the match automatically ended (irrespective of whether the referee blew his whistle or otherwise signalled full time) at the point when the ball ceased to be heading goalwards as a DIRECT result of the kick being taken,
Chris
(Class 1 ref)