they are literally a top 10 team, they qualified for the Blast fall finals and they look prepared and ready for the major, why would they put themselves in A tier? They need the confidence and optimism for the Major..
S tier is top 5 and above. Strong A is a team in top 10. They are well known for choking so its better to stay humble. Confidence is very different from being delusional. Right now the only S tier teams would be Navi & Gambit.
Your definition of S tier isn't the definition for everybody else, the Liquid players think they are S tier and I think they are too, because they are one of the top tier teams who can compete at a very high level
You may not think they are S tier but I do