It's an odd analogy. Musicians frequently advance by learning multiple instruments and genres. Your drums example is good, and there are lots more. Piano's a very common instrument to start with, because it teaches you a bit of everything: rhythm, melody, harmony, coordination, sight reading, and leads easily into learning music theory, and musicians on all instruments often have a piano background. I don't know a single concert violinist that isn't at least competent at strumming out a few chords on an acoustic guitar. Woodwinds players often follow a path of increasingly difficult embouchures, e.g. recorder -> flute -> oboe.
And learning varied "easy" pieces is exactly how anyone practising one instrument advances! The whole grades system used by the RCM is founded on that idea. What's "easy" to you at the time increases slowly with practice, but you learn a variety of pieces in a variety of genres that's at the level you're currently comfortable with.
If someone's going to pick an analogy, they should make sure it doesn't support the exact opposite of the point they're trying to make.