3678 packets / 2.5 hours = One packet every 2.44 seconds * 1500 byte MTU = 3.5KB/s Yup, a 4800 baud modem.
I just checked wikipedia and there's indeed a protocol for them, but I've never seen one in the wild. In my day it was 300, 1200, 2400, 9600, 14400, 16800, 19200, 28800, 33600, 56k ...
So, back on topic, wouldn't it be more likely he was channel bonding two 2400 baud modems?