I've seen some say yes as to that—as an objection to gun control laws, not as an objection to the man's actions—but I don't think it's quite right.
It's true that Oregon law generally criminalizes gun possession on school property, including by people with concealed carry licenses, if the school board adopts such a no-guns-allowed policy. And apparently the Bend school in which the shooting took place indeed has such a policy.
But Oregon law recognizes a so-called "choice of evils" defense, often called a "necessity" defense, that allows people to violate a wide range of laws if it's genuinely necessary in an emergency:
