It used to link to Putty _and_ to the domain owner's competing software:

https://web.archive.org/web/20170822083048/http://www.putty....

The domain owner seems to feel he was providing a service to putty by providing the short domain name and feels slighted that they are moving to have their own now that he is taking actions that they find more objectionable than just also linking to his competitor, but to be honest it always seemed some unethical squatting to me, based on the Putty devs not having the time to complete a UDRP process.