I was out for a ride today and came to a stop light... I was 1st in line in the left turn lane and I looked down at my computer... it said I was going 99.9 mph, my distance was clocking, and the time was moving. I was at a complete stop.

What gives? Is there some sort of signal with stop lights that would interfere with it? It's a Specialized computer and it's wireless...

Bike computers rely on magnets to sense wheel rotation and radio waves to transmit the information (if they're wireless). Traffic detectors at stop lights are basically giant electromagnetic loops. It's conceivable that the loop was somehow interfering with either the magnetic rotation sensor or the data transmission itself. I've never encountered such behavior with my Sigma computer, though.

It's interference, and it's a common problem with wireless computers. I had a VDO MC 1.0 wireless that used to get interference every time I leant it against a shop window while I went inside. Another I had used to get interference riding through industrial areas. When I get around to buying another cycle computer, the first requirement is going to be that it's wired.

Mine recorder maximum speed of 221 km/h yesterday

I've had similar experiences with my Cateye wireless. After I pedal away from a traffic stop, my cadence meter stops functioning until I reset it, very annoying. Purchased a Sigma 1909 STS last year, also a wireless model, to replace the Cateye. The Sigma computer is superb, I have absolutely no issues with this unit at all, anywhere.
Plus thier customer service is top notch, I still can't believe the trouble they went thru to get me a WHOLE NEW replacement computer when I had called them to purchase a button I was missing when my computer flew off my bike during a crash. Great products and even greater customer service!

You've answered your own question. That's what wireless computers do. Try riding under those large power lines some time and see what kinds of speed you'll record.