My proposition is that likes are very different from the non-verbal responses you describe.

Non-verbal responses can only happen in 1) an existing conversation with 2) a small group.

Likes often happen 1) in place of conversation and 2) within a large group.

A like could be given drive-by by any of your 1000 connections at any with no other engagement. That is nothing like "uh huh" and head nods. In fact, if someone outside your small group conversation interjects an "uh huh" randomly while walking past, it's a bit rude.