Was this wallet generated by Blockchain.info ?

If someone somehow compromised your private key, they certainly wouldn't be sending BTC to it. But there is one plausible theory to what could have happened. Previously, certain Android-based wallets suffered from a security breach caused by weak native random number generators. It could be that Blockchain.info has a similarly faulty RNG or RNG seeding mechanism that somehow ended up generating the same private/public keypair twice - either due to a significantly lower than expected level of entropy, or because of a reused seed. These things are incredibly hard to debug, but it would be very, very bad if it were true.

Say for example that the RNG was naively seeded with the timestamp of the system - two wallet addresses generated at the same time, rounded to the exactness of the system clock, would be identical. I would strongly suggest they audit the code to make sure this isn't how it's done.