That homes are being paid for in cash doesn't indicate that there isn't a housing bubble -- it does mean that if there is, its not likely significantly an effect of a mortgaged-backed-securities bubble the way the pre-2009 national housing bubble was.
Sure. But other things could, too -- bubble-driven overbuilding of new housing and then having the influx of jobs stop could do it, especially if updates to shared infrastructure were deferred and the tax revenue to support them didn't materialize because the growth stopped -- the new houses would sell at lower prices because the new higher-paid workers they were made to appeal to wouldn't be there, but the total infrastructure demand would be similar, adversely affecting property desirability.
There's probably other scenarios -- and I'm not saying it is a bubble or that any particular popping scenario is likely (I don't know Austin that well), just that the fact that purchases don't seem to be mortgage-fueled doesn't mean that there isn't a bubble.
My friends here want me to tell you that 'Austin is Full', but everywhere you look there are help-wanted signs.
Which means that housing will be tight until the builders can catch up. Unfortunately, Austin's roads and other infrastructure weren't designed for this influx and are overwhelmed. The city leadership recognizes it's a problem, but haven't been able to produce a coherent plan for solving it. Don't move here.