These huge predators are known as krayt dragons and their bone-chilling howl is enough to send even ferocious Sand People skittering for cover

That doesn't mean that Obi-Wan's howl was that of a Krayt Dragon - don't forget, "Sandpeople are easily startled"

Maybe they saw his lightsaber and had flashbacks to the Tusken Raider legend of this guy who single handedly killed a whole tribe of Tusken Raiders with a 'laser sword'

Now that's a neat idea...

The official name of the ep 3 lizard is a Boga... at least from what I could find online.

That's that particular creature's name, I've discovered - she's a varactyl, according to http://www.starwars.com/kids/activity/draw/f20050325/

DE