Piquionne's header put West Ham 2-1 up against Everton after 84 minutes at Goodison Park and appeared to have secured only their second away win of the season to lift them out of the relegation zone.
He ran to celebrate with the travelling fans but was shown a second yellow, then a red, by referee Peter Walton who has shown eight red cards in 18 matches this season.
The 10-man Hammers were then forced to settle for a 2-2 draw after Marouane Fellaini's last-ditch equaliser for the home side.
Grant, who was told by the club's board on Tuesday that his job was safe, was angry afterwards as his side remained bottom.
"It's a joke," he said.
"What is football all about ? It's all about emotion. We are not computers. Freddie did the right thing, he went to celebrate with the fans. I need to check who created this law. I don't like it. Emotion is part of the game and we should encourage it," he told reporters.
West Ham, desperate for points in their battle to avoid the drop, went ahead after 26 minutes when Jonathan Spector scored before Diniyar Bilyaletdinov equalised with 13 minutes to play.
