Michaelangelo Venti Spray Paint Art Robot Development Halted?

I make no secret that I got a lot of inspiration for the Makelangelo from Jürg Lehni’s Hektor. I wrote to him in July to let him know how much I admire his work and ask questions about how he made his machine so I could improve the kit. After a bit of back and forth Jürg said

I have given this a lot of thought since our last exchange, and have come to the conclusion that I cannot see a collaboration in this. I am therefore asking you to stop making a copy of Hektor, and licensing it under GPL. If you are a fan of my work like you say, then you should respect that decision.

Now I’m confused. According to the GPL,

Software under the GPL may be run for all purposes, including commercial purposes and even as a tool for creating proprietary software, for example when using GPL-licensed compilers.[41] Users or companies who distribute GPL-licensed works (e.g. software), may charge a fee for copies or give them free of charge.

Makelangelo has been released under the GPL since the beginning. So is Jürg saying everyone except me is allowed to make copies and sell them? Some of my more successful friends have told me that, legally, I don’t have to do anything, that I should ignore Jürg and just keep going. I want to be a good person and do the right thing. I want to make for a living making robots people love. I want to sleep well at night.

The nice thing about having many robots is that I can let one go and continue in another direction. I’d be a little sad if I can’t help people make more public art. The world needs more beauty.

I hope this also sparks interesting conversations about artist’s rights, open source, and commercializing maker work.