It also adds [solved] to the end of the title. (I've marked this one as resolved to illustrate it.) Which helps people searching for threads. If you google an error message and see "solved" you might be more inclined to clink on that link.
I have seen a few topics -- which has no responses -- and has been marked as resolved..... Obviously, if the OP is still interested in the topic (meaning clicking the resolved button in error), this is kinda unfortunate, as you are telling those looking for questions to answer to move on.
If you are not seeing answers to your topic, it may be a good idea to ask a moderator to undo the resolved status.