I will call it:

Coincident.

And this is not the only time it happened but it happens quite frequently and there is a term for such films: Twin films.

Similar example is No Strings Attached and Friends with Benefits. Both tackle the same subject and from same genre romcom. Also it happened with Hercules and The Legend of Hercules which both centered around the same demigod.

We don't know the exact reason why it happens but there are some speculations:

Some attribute twin films to industrial espionage, the movement of staff between studios, or that the same screenplays are sent to several film studios before being accepted. Another possible explanation is if the films deal with topical issues, such as volcanic eruptions, reality television, terrorist attacks or significant anniversaries, resulting in multiple discovery of the concept. *

Even Disney and WB almost did it with Jungle book story but then WB pushed it for later and renamed it.

BBC explain similar cases in there article and the most controversial one is:

A Bug's Life & Antz

A row broke out between Pixar bosses Steve Jobs and John Lasseter and DreamWorks CEO Jeffrey Katzenberg, who had left Disney's film division to set up a rival company. Jobs and Lasseter claimed Katzenberg had stolen their idea, which Katzenberg denied. The press revelled in how dirty the fighting got, with Katzenberg bringing forward the release date for Antz by six months to beat A Bug's Life into cinemas. Antz was a box office success, but it didn't harm the Pixar film which eventually made more than twice as much as its rival did.

Similar posts:

Why are two Jungle book movies being made consecutively?

Similarities of Pixar and Dreamworks: any published explanation?

It appears just to have been a coincidence

Sometimes writers just happen to be working on movies at the same time with little to no knowledge of similar projects.

The Illusionist and The Prestige are not very similar movies, but they do suffer that stereotype because they’re about stage magicians and happened to be released near the end of 2006. Apparently Christopher and Jonathan Nolan had been working on the screenplay for years and finally finished it in time for the Fall movie season.

Whereas, The Illusionist won over crowds in early 2006 at Sundance and was bought for release which coincidentally happened two months before the Prestige.

^Source

This is not uncommon.

Obvious examples are:

• Volcano & Dante's Peak
• Flight 93 & United 93
• Armageddon & Deep Impact

On at least one occasion, movies were based on similar books and two studios co-operated in making one blockbuster movie rather than cannibalise each others profits.

The Towering Inferno

Warner Brothers outbid Fox to obtain the rights to Stern's The Tower for $400,000. Fox, in turn, spent $300,000[14] to obtain the rights to Scortia's The Glass Inferno. Irwin Allen realized that two films about a tall building on fire would cannibalize each other (as actually happened a couple decades later in the case of the two films about active volcanoes, released nearly simultaneously, Volcano (released by Fox) and Dante's Peak (released by Universal)[15]), convinced executives at both studios to join forces to make a single film on the subject.

^Wikpedia