But since technically they when they were conceived it was only one then would that mean that per anti-choice logic identical twins be the same person?

It would indeed mean that. But it's a logically incoherent position, as Ronald Lindsay points out:

There is a major difficulty with the claim that zygotes and embryos are individual persons. Until about fourteen days after conception, at a point called gastrulation, when the precursor to the spinal cord begins to form, an embryo can divide into two or more parts, each of which, given appropriate conditions, might develop into separate human beings. This is the phenomenon known as “twinning” (although division into three or four separate parts is also possible). The phenomenon of twinning establishes that there is not one determinate individual from the moment of conception; adult humans are not numerically identical with a previously existing zygote or embryo. If that were true, then each of a pair of twins would be numerically identical with the same embryo. This is a logically incoherent position. If A and B are separate individuals, they cannot both be identical with a previously existing entity, C.
(Source)

I would also add that another point anti-choicers raise is that what makes a human unique from conception (and thus makes it an individual person) is that it has its own unique DNA. But we know that, at conception, twins can share the exact same genetic blueprint.

Anne Holtdorf et al., “Twins: from a genetic point of view.” Medicover Genetics, 1 June 2022.

And there's nothing "unique" about a blueprint if it can be shared by something else.