No. A single statement can never be gaslighting. Gaslighting is a process. Being told to be wrong (even if you may be correct) is not gaslighting either. The important element is to plant doubts about your _perception_.
I am your friend, trust me.
"I spoke to everyone" is, by definition, not a single statement.
Everyone telling you you're wrong definitely can instill doubts about your perception.
Continously being told to "be wrong" can instill such doubts, but more precisely it would be me worrying about you "seeing it wrong", not accusing you of _being_ wrong about something. Your quote does not necessarily carry that meaning.