Is it correct to state that Contractor’s liability for defective workmanship ends with the expiry of the Defects Liability Period?

No, is not correct. When the "defects liability period" is in force, Contractor has the contractual obligation to return to the site and repair defects which has appeared in the works. Depending on the contract, the Contractor may also have an exclusive right to repair the works during "defects liability period".

The end of "defects liability period" is not the end of Contractor's liability for defects as a result of defective workmanship.The owner of the works - which can be a different one than initial contractual party - has the right to sue the Contractor for instances where the construction work does not meet the specification, accordingly to the legal obligation of the Contractor to rectify defects, legal obligations that can be found in the governing law of the contract.