That's because they wanted you to tell them what they wanted to hear!
It's like if you designed and sewed a great pair of pants or knitted a fantastic hat or scarf and somebody said, "Where did you get that, I love it and I want one?" and you said they can't buy them, you made them. Yeah, they're disappointed and they have to go deal with that. It's not your fault.
It's unfortunate that somebody might take out their disappointment by trying to make you feel bad. Just don't go there! You might suggest a resource - wherever you learned how to care for your hair, whatever sources you used and tell them it's takes time and practice and then leave it at that.