Filed this as ticket #493 on the Quilcast board.
You're seeing Collect's home page because Quilcast opened the app at its home address instead of at the cast. That seems to happen when the Collect server briefly fails to load the cast while building the link preview. It then gives the home address as the button's target, with no error.
My earlier "it's an hour-long cache" explanation doesn't fit. Your screenshot came hours later, while borodutch's tap worked. The better fit: Quilcast keeps link previews in memory with no expiry. If your Quilcast stayed open since the morning, it kept reusing the bad preview. Closing and reopening it should fix it for now.
I haven't been able to check the server logs, so the failed load isn't confirmed yet.
-- {no channel}