1. Yes, it's true if the contract or scope of work exceeds $500 in value;
2. Technically, he/she could record a lien but if they were not properly licensed at the time the work was performed, then the contractor's lien would be nvalid, they aren't entitled to recover any money and the lien could be expunged via petition to the court.
3. The owner cannot escape liability for the lien unless a proper Notice of Non-Responsibility was timely recorded and posted. Furthermore, if the rental agreement requires the tenant to make the improvements, even a notice of non-responsibility might not help the owner.
4. You can file a petition to expunge the lien.
5. Yes, you can file a complaint with the contractor's state license board.
6. Since this was commercial work, a written contract isn't necessarily required. If the contractor was licensed, then he likely could record a lien.
The short answer to your question is: no. An unlicensed contractor does not have lien rights. In fact, an unlicensed contractor does not even have the right to collect payment on the contract even if all the work was performed. If a lien is placed on the property by an unlicensed contractor, a written demand to remove the lien should first be sent. If that doesn't work you may sue to have the lien removed and recover damages plus reasonable attorney fees.
No information you obtain from this answer is legal advice, nor is it intended to be. No attorney-client relationship is intended or formed between the questioner and answerer. You should consult an attorney for individualized advice regarding your specific situation.