250TB/month is still way, way below "unlimited" though.
(If you're really lucky, you might be able to get 900Mbps or so, but that's not likely: the max throughput on 1Gb Ethernet is below 950Mbps, even if you had packets flowing continuously!)
They also said the use averages above 250TB.
It averages on multiple of their servers, which indicates to me that the average was taken over the course of some months (?). They may well have reached 320TB in some months on some servers.
I'm not surprised by this. For me, unlimited traffic (with 1 gbps) means i can spike in some months without having to worry about costs exploding, but if I'm maxing it out consistently, then I might be asked to move to a different service or upgrade.