Fair, but does that mean that the entire article is speculative? They were not around long enough to confirm whether or not it happened for days, but the fact that the mother stayed for at least some hours appears to be confirmed (although as another reply said, the motivation for staying could be different than ours).
You will likely find a lot of these hedging comments in scientific articles, as it’s hard to know and prove something with 100% certainty and it’s an important task for researchers to also indicate the limits of what they’ve discovered. I think ;)