The Manchester City manager said that he has not spoken to Aguero about the incident as he believed that the striker's contact with Massey-Ellis was not aggressive.
Guardiola insisted that Aguero's intention had been simply to talk to Massey-Ellis, having disputed her decision to award a throw-in to Arsenal during City's 1-0 win at the Etihad last weekend.
The laws of the game state that any "physical or aggressive behaviour" against a match official is considered to be a sending off offence, but Aguero was not punished either during the game or retrospectively.
The Argentina international was criticised by Match of the Day pundits Alan Shearer and Ian Wright for the incident, among others, but Guardiola said he had not spoken to his player about his conduct.
"I know perfectly Aguero, it’s like what happened with Bernardo Silva and what he had with Mendy," the City manager said. "They are brothers and [Bernardo] was suspended."
"All the people looking from outside judge, I know the intention from Sergio.
"Sergio put his hands in a normal way like he does many times to me, on or off the pitch or when I hug him, when there is a substitution or when sometimes he touches the referee as well or an opponent.
"If I’d seen some aggression, maybe. I think it was normal as I know him perfectly. He’s been a huge star in the world but he’s humble, nicest people I've met.
"What is important is his intention and his intention was normal, to talk to her in a normal way, it was not a bad word, it was just normal.
"I didn't speak to Sergio about this but I'm pretty sure if she felt bad he will apologise without a problem.
"It is the same what happened with Bernardo, I know him perfectly well and it was a joke and this was a normal situation."
Bernardo was suspended for one match and fined £50,000 last year for a tweet which compared Mendy to the mascot of Spanish confectionery brand Conguitos.
The City playmaker was accused of using a "racist stereotype" by Kick It Out, the football anti-racism body, but Guardiola defended the post as a joke between friends.