I keep a very polite attitude at all times and expect the same of everyone else to do so to me. If not, then we will not be working with each other for long. When an employee gets upset at me, I simply don't retaliate back at this employee and escalate a situation in the work environment.
To my mind, you are not turning the other cheek here. When one doesn't enter into an escalating situation, turning the other cheek is not implied by that behaviour.
In some cases the employee can be trying to bait you into getting some kind of confrontation, but you don't have to go there - just like one doesn't have to reply to a troll on the internet
So, well done to you for not going there. I know from my own experience in middle management that it can be difficult at times to keep your calm when dealing with people. These days, having a manager who is younger than me, I find it interesting to not some of the insecurities I had myself in him and seeing him do things that I did myself but later found to have been counterproductive.