I can follow the logic of showing “Have you tried the %{heart} button?” on too short replies, but it is confusing to show this error message along too short opening posts IMHO.
What should I like instead of opening a new post of a non-existing topic (which I can’t like)?
Also, the mindset is bound to the composer… so the user will look for a 
button in the composer, which obviously does not exist.
This implies I can somehow solve the too short message by clicking the button.