From your review, it seems possible you are perhaps not very experienced with the ins and outs of the industry or the information which is common knowledge on this board, or the nuances of tone in writing text (in the context of north America and especially Quebec)
(please don't take that as some kind of attack, it is just an impression).
Yes the response from the booker was rude, but please take this with a grain of salt, and learn the essentials:
If you contact an SP or Agency, and they only list hourly rates, do not ask for a shorter session - this is seen very negatively. I believe for most here this is obvious.There are very negative connotations of sessions under an hour . With a reputable agency, you should not ask such a question - especially if it is clear they do not offer this on the website.
Everyone else made some good comments about some key lessons to learn from this.
Also, from my perspective, to be blunt, your message wasn't very polite either, especially if you compare to how other experienced clients write very friendly and informative message. Your message might have irritated to the booker if they usually get polite message from regulars. Say what you will about the value of being concise, but being polite and well spoken, goes a long way, especially in this industry.
Your message lacked tact. The agency is as much concerned about filtering out potential bad clients and prioritising the best ones, b/c their SPs are going to deal with the client in the most intimate way. The bookers are very experienced and have a good sense of how to "read" people from their texts. It is in their best interest to filter in only the best possible clients, as for every one of your type of message, they get twenty much more appealing ones. So try to understand it from their perspective. They are protecting their SPs and their business.
The booker's response was rude and offensive yes. Maybe they had too many irritations that day or the previous, and this pushed them over the edge.
I wouldn't write-off an agency for such a response, considering your method of contact. Try to "not take things personally", just friendly advice - as others said very well, text communications have really hurt the way people treat each other.
I hope you can take this feedback in a constructive and elegant way, without being defensive, and value the other possible side of how a situation looks to others.
FWIW from almost 18 years experience in the scene, usually the most polite are the indies aged 28+ at 300$+/hr range, and agencies if you're a regular or CALL on the phone. If of course, you contact them exactly the way most of them guide you to on their website.
To close, I'll say, I can absolutely imagine how unpleasant that remark from the booker must have been, bad enough to ruin a day.