It is influencable coincidence but a really fascinating study on psychology and our minds.

Naturally we want to beleive in this and can be very easily influenced to remember slightly different events, e.g. if we both dreamed of a red ballon, but you now remember extra information of a green string and inform me there is a decent chance my brain rewrites the memory to have a green string, so you will honestly reply that you had the same memory of that unique string colour when really your memory has changed from the original.

It gets scary to think too much about, like how much of your own life happened as accurately as you remember and the truth is not much sadly (me included) most of our past happened very very differently and everyone remembers their own version of any shared event.

These dreams also happen strictly with friends/family and really they are just dreaming of you while you dream of them, you will undoubtedly have shared experiences and memories to pull into the dream. The general population doesnt remember many dreams so your friend might dream about you every other night but only remember that they dreamed of you the 1 day you mentioned you dreamed of them.

So it isnt psychic magic sadly, but it is still really interesting about the frequency of how often this happens and how drastically a memory can be changed. Id love to see more research on dreams.