It's most likely nothing, I know when I'm cleaning I'll pick up my candles and place them on a nearby chair or shelf and sometimes it could be in a triangle because of how I picked them up. There's very little detail, is this a friends house? Were you asking someone if they were a witch? Was this your house? These could factor into figuring out if it was a joke, coincidence, or ritual.
It could be a ritual as people do personalize rituals and perhaps a triangle is a symbol they use in their craft, but I doubt someone preforming a ritual would place candles on a chair and walk away. Most people would place candles on a safe surface and find a little more privacy.