I normally use a stainless steel tea ball or other stainless mesh items that usually have a lid so the loose tea doesn’t escape into my cup. Upon seeing your Q, I headed over to Amazon to see what they have to offer. In most cases, I found the stainless steel mesh containers were the main infusers offered. Continuing to look, I did also find an empty unbleached paper mesh tea bag with 100 to a box that was also called an infuser. In my mind, it’s an expensive tea bag with a clip to hold it closed.
I don’t know what your friend meant to send you but I don’t think that they ordered what they thought they were ordering. Personally, I prefer the stainless mesh enclosure for my infuser. I find that I get a much more wholesome flavor than using a simple tea bag!!!
My personal favorite is the little glass teapot with the stainless infuser built into the pot It will make about 3 maybe 4 cups of tea at a time!!!