You have updated the timestamp for the activity Phone Calls using Mass data Maintenance.
After the update the Timestamp shows different than what you had added in the template as per your Timezone.
Reproducing the Issue
1. Go to Mass data Maintenance workcenter
2. Select Import Phone Call link to update the timestamp.
A timezone is set when the task Phone Call is initially created. Hence this timezone will be used though it is not visible in the UI.
Therefore during update, regardless user's timezone, only already stored timezone is used.
Scenario1 : If the data is initially uploaded into the system via migration workbench, the default timezone will be set to below : UTC + 00:00.
(UTC+00:00) Burkina Faso, Bouvet Islands, Cote d'Ivoire, West Sahara, Ghana, Greenland, Gambia, Guinea, Guinea-Bissau, Heard/McDon.Isl, Brit.Ind.Oc.Ter, Iceland
Also you can check with Timezone ,with this timezone the time will be shown as daylight saving with one hr difference:
(UTC+00:00) Greenwich Mean Time with daylight saving time (UK).
Scenario2 : If data is manually created initially by the end user from UI, then the end user's timezone will be stored.
This is expected system behavior as Migration tool only supports UTC + 00:00 during migration.
KBA , SRD-CC-FED , Feeds , How To