That's not what's happening at all, it's similar to regular logia intangibility sure but there are clear differences
First of all, we see two Ryokugyu's on that panel, show me a single time another logia created two bodies of themselves and moved between them.
Second, the emphasis on the plant dying and then being revived is clearly important here, obviously it's suggesting Ryokugyu "died" and then "revived" in a new body.
Why is this important? Because it implies that if the attack was infused with haki, which negates logia intangibility, he'd have been completely destroyed by the attack.