Can observing Shabbat be purely cultural for some people, or would you only do so if practicing?

Non-Jewish atheist here, kinda had a few traditions sprung on me recently that I just rolled with out of respect, but was a bit confused by the whole scenario and didn’t want to prove at the time. There was only one Jewish person present (the host) in a small group of people, so there obviously wasn’t an issue including others as far as they were concerned but seemed odd to me for something religious like that.