Pfff... pretty weird situation. On one side, Max did not lie when directly asked.
On the other side, no one asked him about the legality of how those people were being paid. This is where his characterisation breaks.Seriously, didn't he notice that Allison has turned from a professional superhero into a social justice warrior (and seriously, how the hell did this definition become deprecated and derogatory, it sounds like a compliment to me)? He could have glossed over it, and waited until Ali got inquisitive, or even just joked about it until Ali gave up.
Max getting upset is OK from a storytelling perspective (not from a RL "decent behaviour" perspective), since it gets things moving and is the first part of his real character we get to see.

My sixth sense tells me that he actually doesn't have the authority to send people home, since he isn't the guy paying them.

Another problem is that, TBH, I don't really get the whole deal - how is it a good idea to have them stay there until late? Pay them for the job when the job is finished, even if it takes a few days. I have never, ever seen anyone doing this work during the night, although things may be different in America. Is there a hurry to get the garden in place? As if that kind of garden didn't require constant care, rather than just a few days at a time. And the added risk of incidents during the night, with commonfolk and police officers asking themselves, "how did that guy lose a hand in there?", and the fact that gardening machines are loud.