I don't think it's quite as arbitrary as you're making it out to be. I haven't perfectly defined the concept of a task here, but a core concept of ML is that it's focused on the the learning itself rather than producing a solution to some problem statement. The idea of learning implies an element of generalization, but that's different than general applicability or usefulness. The agent working on the task is our abstraction layer; our algorithm should work on the agent rather than producing the solution to the agent's task. Through some defined process, you're to create a generalized form of knowledge in that agent, without solutions for specific cases being explicitly programmed.

If you train a NN to generate a representative knowledge model that solves a "simple" problem that could have been solved with an explicit solution, you're still doing ML. It's not about how complicated the problem is to tackle, or how generally applicable or useful the result is, but whether what you have explicitly programmed is the direct solution to some problem, or is itself a modeled form of learning that can be applied to some agent that can then go on to solve the problem.

In the Strandbeest example, the program that is running is not modeling any learning. There is no agent. The output of the program is a direct solution to the problem rather than some embodied form of knowledge an agent might use to solve a generalized form of the problem. It's not ML and it's not a fuzzy question, at least in this case, imho. There could be perhaps be cases or situations where there is more fuzziness, but this isn't it.

Optimization, including heuristic optimization as in genetic algorithms, could find applied use in ML, but they are not themselves ML, and the use of a genetic algorithm to solve a problem explicitly is not ML.