When playing Melbourne, the first ‘tram’ update will always show the additional explanation. For every other update (carriage, tunnel, bridge, line) this is not the case. Also subsequent tram updates don’t show the text.
The extra text was shown for every update, until it had been chosen for the first time. I think his registered by the game for all updates except ‘tram’, as the text returns when mini-metro is restarted.
The different behaviour just caught my eye, it is not breaking anything, it was just different. Print-screen for clarification: