Is this the centre of the stem of a mushroom or different kind of mushroom? This long skinny mushroom appeared on the cutting board. I'm not sure if it is from the centre of the stem in the picture or a different kind of mushroom. I'm a bit worried about a stray inedible mushroom but I think it's from the stem but not sure. It's a bit water-logged because I wash them. The other stems are white and woody and don't look like the brown one on the left. If it is from an inedible mushroom is it safe to eat the ones that touched it? (Sorry photo is so big).
This does look like the centre of the stem. Often when I separate the stems from the heads, the centre of the stem would stay attached to the head, It looks just like this.

In any case, if you're buying your mushrooms from a reputable source, you can be sure there are no poisonous mushrooms accidentally mixed in. Cases of mushroom poisoning occur mostly when people gather their own mushrooms and mis-identify them, (or buy from someone who gathers wild mushrooms and has erred with identification,) or, more rarely - when one allows mushrooms to go bad.