Guys, Is my coworker being inappropriate?

He is very shy; and when i first started, he would reach out to me & ask how i'm doing every couple of days. We met in person (our offices are in diff countries) & he didn't talk to me at ALL. But as soon as i was home, he msged me "sorry if i was really introverted" - & now we have regular off-topic convos late at night- 10 pm ish & he always keeps the convo going. Is that considered inappropriate?

Updates
10 mo
Does it mean he's attracted to me?
Guys, Is my coworker being inappropriate?
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