salam alaikum, when my friend was 13 he seen Imam Ali (a) in a dream. He asked imam a question and said Imam Ali has alot if followers today. then Imam went silent and looked sad. what can this mean?

Walaikumussalam
This is the reason for delay of the zuhoor of Imam Zamana as
Meaning is clear that we are so called shia but we are not a true shia and Imam Ali is unhappy with his followers. We must start practicing and changing ourselves.
Wassalam