AirTran's crew probably reported it in the form of an ASAP report. If they thought they were going to get violated for it, it was the only chance they had to not be. There is always a chance that the ASAP board could deny the report and that can leave the crew hanging out to dry. The amount of departures and and takeoffs going on at Seatac can get busy and tower can miss when aircraft do things. Most of the time when your holding short of 16L, right as the aircraft departing 16L passes overhead they clear you to cross. They may have just thought airtran was fast. Or in the case of Low Vis ops it can be hard to see.

Its kind of a guessing game but in 2 years of flying in and out of SEA I had to hit the brakes on 2 diffrent occasions when a captain thought the tower had cleared us to cross and it hadn't.