It is (as @Han Solo says ) the correct interpretation of the rules, though it seems an incredibly harsh punishment for an accidental infringement.Even if you accept that it was a double kick, it was clearly not deliberate, why not a retake? Why disallow the goal for a slip? Very much a check the club badge decision for me.
If a keeper saves a penalty but is found to be 6 inches off his line, the rule is not to award a goal - the penalty gets retaken and he get an second chance to try to save it. That would seem the obviously fair and reasonable outcome here.