Hi CMitchell,
This can be confusing the way the legislation is worded so this may be why you were given two answers.
Please refer to:
CG73550 - Residential Property gains .
But also directly to the legislation at Taxation of Chargeable Gains Act 1992 (legislation.gov.uk)
It would be classed as a residential property where 'the interest in land subsists under a contract for the acquisition of land where a building is to be constructed or adapted for use as a dwelling.
It then goes on to clarify the basic meaning of a 'dwelling'.
It can become complex and all we can do is refer you to the guidance and legislation as we do not have the full facts of the contact/agreement etc and you may wish to seek independent financial advice.
Thank you.