Unbelievable!

Just luck, but it is weird that recently, many people are asking questions about hatching.

If you have a large enough sample size, RNG ends up doing some crazy stuff.

I also caught and hatched my first tangela in the same day (hatched first though) was pretty cool.

Same happened to me in August with Onyx.

He was tricky to catch in the Park I got it...Then in my 10 km egg, Hatched another one.

I was pretty sad that day . Both of them were -80% IV

I think Egg hatching is influenced by where the egg is picked up from. I've had a run of Pinsir from eggs collected at stops at a Pinsir nest, and the same with Kabuto.

Maybe there's a Tangela nest/regular spawn spot currently near where you gathered the egg? was it in the vicinity of where you caught the Tangela?

I had sort of the same with Pinsir. I hadn't even seen on until a few weeks ago. Then I failed to catch one (the game gave me an error). About a week or so later I finally caught one and a few days later I was hatching seven 10km eggs and got three!
Shortly after that I caught yet another one and then hatched a sixth Pinsir before catching a 7th.

So in less than a month I went from no Pinsirs and wishing all the time that I would get one, to getting seven and praying I won't get another one soon ;)

Yup. Odds say this will happen sometimes. Ya get to laugh about it though.