Thrown out of Panda Ball

Can someone please help me understand why Lum can get thrown out out of his Panda Ball (ground B)?

The frame data for Panda Roll is 11/29/8 [24/22] and I’ve experimented with different spacings and frame stepping to make sure that the impact with the opponent is happening within the 29 active frames. So why can the opponent just mash the throw button and throw Lum during the active frames? I thought the point of throws was to punish defensive players?

I don’t have a heap of experience with fighters other than Fantasy Strike, so I might be missing something fundamental here.

If a throw and an attack would hit each other on the same frame, the throw wins. Panda ball is always throwable, so it will always lose to throws.