Well, according to the Information:
Exeter St Davids, Exeter Central, Digby & Sowton, Exton, Lympstone Village and Exmouth
Train operator affected First Great Western
Overrunning engineering work in the Exeter St Davids area is expected to cause disruption on Monday 21 November.
Because of this, the following alterations will apply.
An hourly train service will run between Exeter Central and Exmouth (usually half hourly between Exeter St Davids and Exmouth)
A replacement bus service will run between Exeter St Davids and Exeter Central
Additional bus services will run between Exmouth and Exeter St Davids during the morning peak
South West Trains services are able to run normally, but will call additionally at St James Park - First Great Western passengers may use these services.
Maybe that's why it's over-running. :-/