The message addressed a defensive breakdown late in the fourth quarter that led to a key 3-pointer for Houston in the Rockets' 114-110 victory.
"Getting frustrated about the game, then letting social media get the best of you and giving somebody a response that wasn't to somebody that was relevant to the situation," Trier told reporters after Knicks practice Thursday. "So my apologies for doing that. Obviously, I didn't think he would take a picture of [the message] and post it, but he got his little clout or whatever ... his 15 seconds of fame.
"That's why you don't send stuff like that out."
Trier was guarding Eric Gordon and went below a screen from James Harden. Tim Hardaway Jr. stayed on Harden, leaving Gordon open for a 3-pointer. The shot gave Houston a two-point lead with 10 seconds to play.
Trier wrote in a direct message to a Twitter user that Hardaway was supposed to switch on the play.
"It was supposed to be a switch dumb a-- you think I just let n---a walk up and shoot a 3 smh ya'll 'fans' don't think," Trier wrote in a message that was posted by the user.
Hardaway was asked about the direct message Thursday.
"Oh, so he blaming other people, basically?" Hardaway told reporters. "At the end of the day, I think it all falls down on the team. Team defense, you learn from it.
"I just think that when it gets taken to social media, that means you're breaking the rules of being a team," Hardaway added. "Keep all your frustration and everything and be pros. Don't listen to the outside. We're all in this together, 15 strong. If you let that affect you, then you don't have your mindset and you don't have a clear mind to where you want to go and where you want to be.
"It's a free world. They can do whatever they want. At the same time, I'm all about team and I'm here, I'm here. I'm with the guys -- all in."
Knicks coach David Fizdale said he discussed the social media post with Trier, an undrafted guard who signed a two-year contract with New York in December.
"Just said, 'I know where it's coming from,' because he's frustrated," Fizdale said. "He wants to win. He wants people to understand how much he wants to win and compete. But it can't come out like that. And it can't come out in that kind of anger and frustration, and it definitely can't come out on social media."
Hardaway and Trier also yelled at one another earlier in the game when Hardaway felt Trier should have passed to him on a fast break. They appeared settle the argument in the ensuing timeout huddle and downplayed the incident after the game.
"We were just communicating passionately," Trier said. "Both players care."
The Knicks (10-36) have lost seven straight games and play the Brooklyn Nets on Friday night.