This is because the export on the customer list exports subscriptions rather than the customer records.
This means you might have multiple lines per customer if they have multiple subscriptions or if they have even cancelled one subscription and started another.
Now let's imagine that one of these two customers has more than one subscription. This can be seen by selecting their account and looking for the Subscriptions chart:
This means that when using the export available in the customer list page, it will export all customers subscriptions. Instead of seeing two lines, one for each customer, you will see 3 lines, one for each of this customers subscriptions: