Justin Baldoni's accusation Ryan Reynolds berated and screamed at him in a house full of stars in an ambush meeting is way overblown ... this according to a source who was in the meeting.

Baldoni made several accusations against Blake Lively and husband RR in a $250 million lawsuit against The New York Times ... claiming the "Deadpool" star was aggressive toward JB at a meeting that took place in the couple's NYC home, as celeb pals came and went.

Our source tells TMZ ... the meeting did go down last January, as "It Ends With Us" was to resume production after it was stalled by industry strikes ... and everyone in attendance knew Baldoni's alleged behavior would be addressed ... so, there was zero blindsiding.

The source says RR was not screaming and berating JB, although the source concedes he was "angry and stern," adding Reynold's spoke in an "impassioned" way but it did not rise to the level of screaming or berating.

Baldoni said in his lawsuit the encounter he had with Reynolds was "traumatic" and he had "never been spoken to like that in his life."

The source also took issue with the way the meeting was characterized in the lawsuit ... in particular the mention of the penthouse where other stars were randomly milling around. The meeting was at the home of Reynolds and Lively, but our source says other celebs were not coming and going.

Baldoni isn't alone in suing the Times ... he is one of 10 plaintiffs, including publicists Melissa Nathan and Jennifer Abel, who were mentioned at length in Lively's initial complaint and in the paper's story.

Lively has filed a lawsuit making a formal demand for money, suing Baldoni and others -- including the publicists -- for mental pain and anguish, severe emotional distress, and lost wages.

Baldoni's lawyer, Bryan Freedman, previously lashed out at Lively's claims, saying they were  designed to "fix her negative reputation," adding the claims are "false, outrageous and intentionally salacious with an intent to publicly hurt."