Is this line electrified now? It shows as AC in the Sectional Appendix.
Table GW103-009 States only DM, UM, DR, UR, and ADUL electrified, plus an overrun at Acton West towards Acton Yard, so explicitly not the Poplars on that diagram
Table GW130-001 also does not state that either DP or UP are electrified, which given the GW Sectional Appendix does for electrified lines on every other page I've checked, suggests it is not yet live. Presumably Didcot is noted as the ECR for the AC electrification either because that's the ECR that will be controlling it when electrified, or because on the presence of OLE at Acton Main Line.
I also can't seen any ORR authorisation for placing in service or anything in the PON published on the NR Website about it changing. Could easily have missed something on those though.