Is it ethical to call out of work without giving a reason?

I called out of work today to help my girlfriend and her small business.last night I told the shift lead that I can’t go in today and barely noticed he was asking for a reason on why I’m calling out(I usually have my the work groupchats muted). Is this right for them to ask ? Is it wrong for me to not give the reason I called out? Could I be fired over this? I’m a pretty good worker and hardly ever call out