Is this a bug or something?

Rng all the way.

I've heard some time ago that each pokestop has a increased drop of some pokemon. Have you got them all from the same one?

I've had pretty much the same experience a couple of months ago: 6 10K eggs, 5 Porygons. The eggs were not from the same source.

The same old guy bitching.

Totally RNG. In that same time frame I have only received one 10k egg and it was feebus.

RNG. 100% RNG. I've had it where I hatched 4 Stantlers out of 5 5km eggs. I've had it where I hatched 4 Nidorine Females in a row. I've had it where I got 3 Ponyta, followed by 3 Voltorbs, followed by 3 more Ponyta.

There is something in the Niantic code that causes clustering. Sometimes it is annoying and useless - 6 Porygons - sometimes it's awesome; I've had clusterings of Larvitar and Dratini, Geodudes, Machops and other useful Pokémon, where I hatched 3 in a row of each. (or in the case of the Geodudes, 6 in a row. Every one of them was in the 70's for IV, none of them had Attack as a highest stat, so each and every one got Transferred.)

RNG, man, RNG. Bitch about the bad, but then dance for joy when it's good.