"Él es mesero y actor."
Translation:He is a waiter and an actor.
He's not a real waiter, being a waiter and actor, sans article. He is just acting like a waiter. Whether he puts on a fine performance and acts like a good waiter or not, I don't know. But he is definitely not actually a good waiter or he wouldn't have to act like one. His main problem is his lack of an article. If he only had an article he could then be a waiter and an actor, both.
Leaving out the "an" changes the meaning. "He is a waiter and actor" implies that he has one job which entails both waiting and acting (maybe a cabaret show?) Whereas "He is a waiter and an actor", means he has two separate jobs/careers. I.e. Like most actors, he is not getting enough work, so he waits tables to supplement his acting income.
This is another example of Duo choosing one particular (and for me previously unheard) word for something. I previously learned that "waiter" is "mesanero" or "camarero". I think that a good part of the Spanish speaking world does not use "mesero", so we should at least be presented with alternatives.
I feel a little lost on this one. In Venezuela, I think my wife's family used mesonero. However I looked it up and found innkeeper, host, and landlord. In a small establishment a host or innkeeper could also be waiting tables. So I am not sure where we stand on this. Anyhow, at 2AM I don't think I will wake my wife to check with her. Where was your exposure to the word?
Spanish does not use the article when simply stating professions / occupations. The exception is when you are modifying it with an adjective. Consider the following...
"Él es ingeniero" = "He is an engineer"
"Él es un buen ingeniero" = "He is a good engineer"
You can find more on when articles are not needed in Spanish here...
Are spanish articles needed when describing jobs? In previous examples, saying, "él es un sacerdote" resulted in incorrect translations. In this lesson, I have already seen two forms of this sentence: one with articles saying, "él es un mesero y un actor," and one this one that does not possess any articles.