That's what research is. It's not homework. No one defines the question for you. You just become curious about some relationships.

If they had asked very specific questions the whole study would be meaningless.

The questions they asked are spon on: "To what extent is the growth of nestling blue tits (Cyanistes caeruleus) influenced by competition with siblings?" and "How does grass cover influence Eucalyptus spp. seedling recruitment?"

I disagree for a study on replication, as people having different interpretations is totally fine then but not really related to replication as such. Many valid answers here to the questions. They studied comprehensiveness or something like that.

Imagine in chemistry they had asked to synthesize a compound given a range of inputs and then see a variety of yields based on different synthesis approaches.

Phrased as "how does X influence Y" makes it sound vague, but I think that the question they asked would be better phrased "to what degree does X influence Y"—they got results which varied along a continuum, but not in random different ways. So the actual questions themselves weren't vague, and the researchers all treated it as meaning the same thing, they just came up with different degrees in the results.

But how does that really relate to replication? What they found out is more like: with interpretability come different results.

I agree (and said as much in another comment). The different groups didn't come up with different effects, they came up with different magnitudes of the same effect. This doesn't seem like a replication crisis.