Not really, a bidirectional link is a link between two things that can be traversed in either direction, if I am at A and follow a link to B I should always be able to follow a link to A. Not just go back to A, as in going back a page in a browser, but if I create the line from A to B then later I get to B in some other way, the link from B to A should be created automatically.
Tags on the other hand are a way of noting that things are related in some way that is meaningful to you. It's quite possible the A and B in my example might not have any tags in common, and if they did they would just be members of a possibly very large set.