[ehavener]

Have the clicks redirect through a twitter server?

[theAnonMe]

impressions are not clicks.

[chatmasta]

No, but impressions do require downloading content from a server, which can be tracked. The trouble would be cases where apps are preloading content, so it's downloaded but the user might not have seen it yet.

[nkozyra]

Or - as is often the case - the consumer is caching api responses for some period.