No, it wasn't an excuse. Thomas Romain posted around mid-March (around the 17th or so) over at CATSUKA that they had only just started animating the opening and ending, since that was when they finished storyboarding. It wasn't an excuse made up later. If you want, I can get you the post in question, since it should still be there.
The problem is that the opening and ending themes generally aren't decided at the start of production. They usually are decided later on in the project. Unfortunately, the animation process for the intro and outro didn't start until very late and near air date. Whether or not it was because of a late decision for the intro and outro, I'm uncertain. However, this process is not restricted to just Basquash! and alot of opening and endings for various anime in Japan suffer from this problem. Usually it could be anywhere from using incomplete animation or using episode clips temporary.
And unfortunately, they could not delay production just so that the introduction was finished. They have a set time frame that they must follow or else they won't get the air time. Unfortunately, this also causes problems such as incomplete animation for broadcast. Most animation being produced in Japan is done as it airs, because of the limited timeframe they generally have to work on the animation before broadcast. Some shows can have a wider timeframe before airdate and allow for more episodes to be completed before this time frame, but Basquash! isn't one of them.
It's not an excuse. Whether you wish to believe that or not, is really up to you. The way Japan's animation system works is different than most countries.