This is probably what happened. Droids see the stealthed tank, most droids have an insane range on their stealth scan. Since healer was using hammershot on tank, healer got instant agro and it looked like the healer pulled.
I stealth up to droids in hammer station and normal questing all the time. I usually stealth, force speed to get behind them quickly, then open with the high damage back attack. You do know that a droids stealth scan is when they drop those mini droids that spin the scanning beams. What you're saying basically is that me being stealth'ed further away from the mob than a heals who's 3 levels lower than me and standing closer to them unstealthed is what pulled them? No way. Please read my posts fully if you are going to respond to them. I offer you the same courtesy.