But it may have been green when he started going across.

One problem is that stop lights are timed so that the yellow is long enough for a car traveling the speed limit to clear the intersection before it goes red and the cross traffic gets their green light. But the yellow light usually doesn't last long enough for a slower moving bike to really make it all the way across a multi-lane intersection. It's green when they enter, it goes yellow, and goes red before they make it all the way across. Drivers aren't really thinking about this and it is a source of potential car-bike crashes.

If you notice, the pedestrian signal goes to "don't walk" way early, while the light is still green, so that people will not start across and get only half way before it turns red. Slow moving cyclists should probably look at the pedestrian signal as a heads-up for how much more time they have to make it all the way through the intersection. Those new ones that count down the seconds are awesome.