I would disagree with that as a general point and certainly as it being something specific to outsourcing.
Bad time management seems to be a common trait in technical people (I know it is one of my key failings) both in terms of simple punctually and in terms of estimating time/effort requirements - this is something you will run into even with a local developer (though the issue will likely be more visible and so perhaps caught and mitigated earlier) and this is why project managers and such exist. It is a different mind-set sometimes.
Also, almost all software projects are not well estimated. Features are missed from the initial spec, testing time is not fully accounted for, "last minunte" revisions are made as issues and new ideas come up during the development time (unless a full spec freeze is insisted upon), and so forth. A project taking twice as long (wall-clock time or man-hours time) as originally expected is not all that unusual.
The PP seems perfectly happy with the work done and the time/effort/cost it took, so I assume there is no accusation of swinging the lead or the underestimating being something that was due to general incompetence.
Outsourcing can work very well for some projects, particularly smallish ones, but you need to be very careful to manage things appropriately or the costs can quickly run away from a manageable place.