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Unfortunately your capture shows only one flow of the TCP connection and does not include the three-way-handshake (for iRTT calculation), so it is not possible to comment on your specific case. But...

In general, when there is a high bandwidth network, there are many packets being send per second. Whenever a packet is lost, all the other packets that are already on the wire will be received and will generate a DUP-ACK. For instance, when a TCP connection fully saturates a 1Gbit/s link with full-size frames, there are about 80.000 packets per second. If your RTT is 1 ms, you will have 80 packets on the way before the first DUP-ACK returns to the sender.