On Saturday, a tournament official told Thiem to leave the room while he was speaking to reporters after his win against Uruguay's Pablo Cuevas in the third round at the Roland Garros.
According to French newspaper L'Equipe, Williams was keen to fulfil her media obligations as soon as possible after her third-round loss to Sofia Kenin, saying "put me in another room, smaller, but now".
"Every player has to wait. It shows a bad personality, in my opinion," Thiem was quoted as saying by the BBC.
Thiem, the fourth seed, had complained to a tournament official at the time of the incident. "What the hell? But it's a joke, really. What's the point of that, that I have to leave the room because she's coming?" he said.
On Sunday, the 25-year-old said he believed Williams had contravened the players' usual protocol. "I wasn't angry or frustrated. Maybe for a couple of minutes or so. It is just the principle," he said.
"It doesn't matter if it is me who sits in there, even if a junior is in there. I am 100 per cent sure Roger Federer or Rafael Nadal would never do something like that," he added.
Federer had earlier admitted the situation was handled poorly by all involved and that "superstar" Thiem shouldn't have been put in that position.
"I don't know what went wrong but something went wrong for this to happen," said the Swiss legend after his straight sets win against Leonardo Mayer.
"If I would have lost today against Leonardo Mayer, I would let him go first or decide when he wants to go to press as he's got a next match. My next match is far, far away. So that's just the way you go about it.
"There must have been a misunderstanding, or maybe they should have kept Serena still in the locker room, not waiting here in the press centre," he added.
Williams has hit headlines ever since she returned to the court after giving berth to daughter Alexis Olympia in 2017. Last year at the US Open, she had accused umpire Carlos Ramos of sexism after her loss to Naomi Osaka in the summit clash, a match that was marred by controversies and penalties.
( With inputs from IANS )