I'm no lawyer Freda. While that would certainly qualify as misleading in my eyes, I don't think that is included in the application of this condition which seems to refer to the information in the "description" supplied. Elsewhere in the T&C doc, "description", while not specifically defined, refers to the description on the website and I think this condition applies to that only. E.g.:
5.8 You are personally responsible for a bid made by You. You may not retract a bid except for limited circumstances allowed under applicable law, for example, where the Lot does not materially comply with the description provided in relation to it on the Website.
So, if that description describes the horse as a racehorse (when it couldn't be because of injury), or 'sound' (when it wasn't), this might apply. I think what was and wasn't said in the buyers due diligence process falls under the buyer's responsibility indicated in my earlier post relating to the Ts and Cs.