Well, were I the hiring manager I would interpret your statements as "instead of me paying for training to improve my own skills, tell you what, you guys pay me to take up the time of your employees who will mentor me, and in exchange I'll abandon you for my better-paying freelance work after I've learned what I can from you". Maybe that's not what you intended to communicate, but that's what I'd hear.
I've had interview candidates who told me straight up that they intended to use the position as a stepping stone to work outside my division or my company; I "no hired" those people. They might be great technical candidates, but if I'm just going to have to find their replacement in six months or a year, it's better to pass on them.
What would be a better way to put it? All I can think of is leaving the salary remark out altogether.
Salary negotiation is tricky. All prices send a signal. "I am taking a significant pay cut" can signal a lot of things, and "you are getting a bargain by hiring me" is not necessarily one of them. Leaving aside the "leave in six months" aspect, this potentially sends signals like:
- My work isn't very good, but you're getting it cheap. Maybe it will get better in the future, and then you're really getting a bargain.
Well, if I wanted that, I'd hire someone straight out of college. I want my industry hires to justify their higher cost by being immediately productive.
- I don't need this job. You guys are lucky to get me.
Signaling that you're willing to walk away from a deal is a powerful negotiating position, but you've got to be willing to do it, and you've got to convince them that they really are lucky to get you.
You know what good hiring managers want to hear? Only two things. Hiring me will make you hugely more revenue than my fee, and hiring me will lower your costs more than my fee.
Now, I'm not saying to in any way be misleading about your motives. But if you're asked again "why do you want to give up your lucrative freelance job to work for us?" then emphasize something that looks more like a win-win. "I want to concentrate on writing great code to solve (business problem X) without having to waste my valuable time that I could be coding drumming up clients, dealing with billing and all the other hassles of freelancing" is way better than "my code isn't maintainable, so I want to learn from your guys on the job".