What does it mean when a man winks at a woman?

yesterday i was having a conversation with a former coworker, male, i’m a female. it was only job related, nothing sexual. we are just friends. it was a very nice conversation, mainly discussing the job we used to both have and how we are happier now. he was in his car and i was standing on the street. he had pulled up when he saw me. when the conversation was over and we said our goodbyes, he winked at me.

i have been winked at by men before. i know (or i think i know) this can be sexual. is it always sexual?