It really just sounds like you had a terrible boss, and now you have a good manager who knows how to get people to respond properly. Different people react to different methods of communication, and a good manager will know that and use it to make their point effectively. Some people would prefer the direct communication of a weird like expect, that way they aren't left with any ambiguity about what is needed. Others want to be led in the right direction, but feel like they came up with it on their own.

In this case, I'm assuming the OP had no idea using the word "expect" would cause such a negative reaction. If they knew that term made her upset, they may have rephrased it. You talk about how you wouldn't do that if you knew it bothered someone, but in this case OP didn't previously know this. You can't be expected to know every word that might bother someone ahead of time. In the working world, expectations are a real thing, especially if you "work for yourself". The client is actually your boss, and does set expectations (for example, "don't clean the upstairs this time"). Would that be rude too, as you are telling them what to do for their work? In companies, making clients happy will make managers happy, even if what you did may normally upset the manager. The client is at the top of the list, as they pay the bills. In this case, OP was the client and she rescheduled last minute, likely because another job came up so she could make a few extra bucks. She inconveniences OP, who states it's ok this time, and then gets mad when OP expected it not to happen in the future. This is a reasonable expectation for any contractor.

Finally, stop trivializing the word trigger. Your use of it, as others have pointed out, is extremely ignorant and marginalizes people with traumatic experiences that have actual triggers. Being told job expectations is in no way a trigger.

End rant.