Popped something on my nipple

So I was changing in front of a mirror and noticed a little bump about the size of a pimple on my boob and squeezed it for a minute. At first noting came out but then it did the second time and a little white string like thing came out. (Please note this is not my nipple but it looks very similar to what happened to mine). Has anyone else had this? Do you know what it is ?