Benitez claimed he was waiting to shake hands with the Manchester United boss but that Ferguson walked past him without doing so.
The Chelsea interim manager, speaking after his side's 2-2 fightback draw, said: "I was waiting at the beginning. It's up to him, I was in the way waiting.
"Ask him (why) if you are brave enough to ask him. It was his decision. I was ready and waiting. I have some education because I know a lot of people are watching so I know what I have to do."
Benitez, whose rivalry with Ferguson stretches back to his time as Liverpool manager, did not attempt to shake the Scot's hand after the conclusion of a match that saw the holders come from 2-0 down to force a replay at Stamford Bridge.
"I was with my players celebrating," the Spaniard explained.
Second-half goals from Eden Hazard and Ramires salvaged the draw but Benitez insisted Chelsea deserved to complete the turnaround, having been denied victory by a fine David de Gea save from Juan Mata at the death.
"We analysed the game and we deserved to win," he added. "The first half we made two mistakes and conceded two goals but in the second half we were on top of them and had a lot of chances.
"They had everything in their favour: they are playing at home, they played on Tuesday, we are coming from Romania (defeat to Steaua Bucharest in the Europa League) and had to travel again so we did a great game and I'm really pleased with my players."
Benitez admitted bringing on Hazard and John Obi Mikel had changed the match in Chelsea's favour.
He said: "We knew that we had to change something and we knew Hazard is a player with quality who can make a difference and he had fresh legs as well.
"I asked Frank (Lampard) to give 100% until then and he did. You have to manage the squad.
"We saw the character and the reaction that I was expecting so until the end of the season we will be fighting."
The winners of the replay will face Manchester City in the semi-finals but such is the fixture pile-up that there is no obvious date for that replay to take place.
Benitez said: "I cannot say when I prefer, we have so many games it depends on the dates. It is an FA decision."
Benitez refused to be drawn on speculation Rio Ferdinand may face FA action after an altercation with Fernando Torres.
"I haven't seen the replay - you can see the replay," he said when asked for his response. "You have an advantage and can do it now."
Benitez also confirmed he had spoken to Torres about the matter but would not go into any details.
"I don't talk about things that happen on the pitch," he added.