I assume the person was in audit based on his career. Tax people usually stay in tax for their career and once you reach a certain level in tax, it's pretty safe but the work is pretty complicated, more than regular accounting.

I think once you get to the interview stage, everyone is treated the same.

Honestly, most people nowadays do not have job security. Even if you are some director level person in  Fortune 500, you could still get laid off and not being able to find a job. I feel like no matter how high you go, you still need to prove yourself all the time, there is no point in time when you can relax. That's how corporate america works.