This part is wrong. A better approximation is OP_RESERVED. If you have OP_RETURN, then the Script is invalid immediately. But in case of OP_RESERVED, it can be wrapped in some unexecuted OP_IF, and it will still remain valid.

But in general, it would be even better to compare it into "OP_FALSE OP_VERIFY", because this is what was intended, when creating OP_RETURN.