Hey guys - long time no see! Hope everyone is surviving this heat wave! 👋

Had a quick question that only my Houzz buds would know.

I bought a tiny little plant that I thought was a fairy castle cactus around four years ago. It was randomly at a drug store in a 2” pot, no label.

The photo on the left is about a year later - when it still looked like the plant I bought. The photo on the right is its current state — much bigger but not what I expected the plant to look like.

Is it not an Acanthocereus tetragonus — or could it be something I’m doing or not doing? 🤔 I have it indoors on a windowsill.