I can see how that happens. No one really checks the date of every thread they post on, but occasionally a list of 'threads similar to this one' comes up at the bottom of the desktop app, and people click on them and respond as though they are new.
There are some longstanding threads where groups of posters follow the progress of the OP - and that's fine and I think invaluable for support reasons. But surely it isn't beyond technological capability to automatically instigate the closure of a thread once no one has posted on it for, say, three months?
I'd say this one was less user error than software limitations.