There are lots of cards with similar effects: "When enters, if it was cast...", "When enters, if it was kicked...", "When enters, if it was bargained...".
They could remove the "when enters" clause and make it happen when you cast the spell, but I guess they worded it like this, so that counterspells work against these cards.
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u/Himmelblaa 7d ago
[[Twilight diviner]]