don't want to put words to his mouth but I think, that it was because less people are familiar with solaris (and other "less used" platforms like aix, hp unix etc) then with some common distro like RHEL, what can run anybody everywhere and obtain the skills much easier..
The he made a false statement. That doesn't make the OS safer nor harder to hack, it makes it inconvenient.
There is a difference.
"Hey I just made DogieOS today, its the most secure in the world because its never been hacked and there are no vulnerabilities." Its the same claims Apple made for IOS and OSX, before immediately getting rekt by 100s of exploits.
Finally.