1.
If you come across something or someone, you find them or meet them by chance.
I came across a group of children playing.
= encounter
PHRASAL VERB : V P n
2.
If someone or what they are saying comes across in a particular way, they make that impression on people who meet them or are listening to them.
When sober he can come across as an extremely pleasant and charming young man...
He came across very, very well.
= come over
PHRASAL VERB : V P as n , V P adv