There is no way this isn't on purpose. They wouldn't expose something sensitive to satellite imaging unless they wanted to.
They track all observation satellites and meticulously schedule aircraft movements for when they're not observed. The problem is Planet Labs alone has over 200 satellites, and that's in addition to other commercial imaging providers and all the governmental earth observation satellites. That means in recent years the margin for error has become increasingly smaller.
Given all that, while it's certainly possible this was deliberate, I don't think it at all implausible for it to be accidental. Some occurrence that delayed them by just a few minutes could potentially have caused this.
I'm surprised that there are still windows of time where any piece of land isn't "seen" by satellite. I thought there was 24/7 coverage especially on special sites like Area 51.
Painfully obvious this is a purposeful leak.
>All that being said, we must underscore that spotting a totally new and exotic aircraft design in the open at Area 51 is largely unprecedented, and for very good reason.