booting an iBook from a live linux usb drive
A quick search for Lenovo ThinkPad shows these machines use Intel processors. I believe your iBook uses a PowerPC processor. So one would expect the USB flash drive to fail to work with your iBook, if you can boot using the ThinkPad.

Appendix

Ubuntu PowerPC FAQ

Lubuntu 16.04.3 LTS (Xenial Xerus)

Ubuntu MATE 16.04.3 LTS (Xenial Xerus)


  Note: iBook (Model A1007) shipped with 256 MB of RAM. This is expandable to a maximum of 640 MB.