To enter Thailand from the UK, your passport must have at least six months of validity remaining from your arrival date, plus at least one blank page; this is a strict Thai government requirement, even if you're only staying a short time under the visa exemption scheme, as immigration officers and airlines enforce it, so renew your passport if needed before flying.
Becouse the TDAC is linked to your passport once you hand that over it all pings up on there screen. If you had not done the TDAC you would have been pulled aside and not let through untill you done it.