Yes, you have found correct information.
Skyvia uses SOAP API for data retrieve. Usually one API call is used for 2000 records.
For data insertion the Bulk API is used. Batch size is 5000 records or 10Mb. If you disable the checkbox "Use Bulk API" in your Salesforce connection, the SOAP API will be used for data insertion, too.
If an entity has a Long Text column, then one API call is used for 200 records. For example, the Attachment entity is also processed in a special way. One API call is used for each record of the Attachment entity. Thus, if you have many records in the Attachment entity or in entities with Long Text columns, import can use that many API calls.
Lookup also increases the number of API calls (as it sends requests for data retrieve).
Please note, all API calls sent to Salesforce are counted, not only Skyvia's. You can check your API call statistics in your Salesforce instance:
Reports -> Administrative Reports -> "API Calls Made Within Last 7 Days"
Setup -> System Overview -> API Usage (API REQUESTS, LAST 24 HOURS)
If you have any further questions, feel free to contact us.