Below is an example of a webhook response and its not matching with what you have pasted. Are you sure you have pasted all of the webhook response. Looks like it is missing the type of event and so on.
When adding fields from grid, if you insert a new record directly on the grid (by not using expand form), then NocoDB Insert webhook will be triggered as soon as the record is created (and hence only ID will be sent as part of trigger response). And remaining changes done on the record will be considered as Update trigger. You can make use of expanded form to ensure everything in the record inserted is treated as Insert trigger.