You don't have to make it easier to know how to use the pickaxe. Do it if you want to, but you explicitly told the player that it can be used to mine rocks and the player would shortly after (or before) see their path obstructed by rocks, I think you made it pretty obvious already.
So I really want to emphasize that I blame myself for that but I also think the random encounters could had contributed because they were too distracting.