Not so different from women that put "I don't know yet". Could be anything really, from what some other female redditor accused (bad intention and lying) or just that they haven't figured out if they want a relationship (and what kind) yet, but still want to date and meet people.

I have "I don't know" because I'm not in a rush for a relationship. If we get really along and click, then sure! If not, well I can just enjoy dating or meeting up now and then. If you'd be exclusively looking for relationship, you'd probably not be too keen meeting up someone you don't see a relationship coming the way.

Met a girl with "I don't know" too that broke up with someone recently, and is open to relationship happening but are not actively looking for it. That's cool, we enjoy going for a drink now and then and play darts.

Point is don't over think it; If you're looking for serious relationship either ask early (before meeting, but casually) or just dont swipe right on them.