BuddyPress.org

imo, It’s not clear what you’re trying to do.
On a ‘single activity page’ – you mean the profile activity page for a specific member ?

And on that page you want to display, in a sidebar, the 20 most recent updates from all users ?

In your code, you’re only looking for updates that include an image [bpfb_images]

So you only want the 20 most recent updates from all members that include an image ?
If so, you’d be better off writing a custom query. Then you won’t have to do all that string parsing.