The landlords were clearly communicating pricing information to one another with the intent of profit maximization. I don't see how software mediation changes that.
Good overview of signaling here - https://www.jonesday.com/-/media/files/publications/2016/09/...
Doing it secretly would invite scrutiny and reason to issue subpoenas though.
What would be the purpose of this meeting other than to make implicit pricing agreements?
Does anti-trust law explicitly require a written / verbal agreement or does doing lots of things that looks like agreeing (without actually agreeing) count?
Not fine: “I’ll set my price to $X if you do as well.”
The hard cases arise when this communication is obscured or implicit.