Diablo III - Imperial gem drops at level ~13?

So I played D3 when it came out for a couple of months and haven't touched it since. I have picked it back up again and started a new character with a friend. I looked up how to get to Whimsyshire since I had a wand of herding in my inventory.

We were about level 13 and ran through whimsyshire. We opened up either some presents or a happy cloud, and out dropped a load of Imperial gems. I thought "OK, I remember gems, you socket them in stuff and you can combine them". It's only after getting back to town I realised that in all the hours I played before, I got to some Perfect Square gems as the highest level, and these Imperial gems are significantly higher level than those, dropping at player level 13 on Normal difficulty.

So my question is... what the hell just happened? Was it supposed to happen? Did they change things that much in the last few years that these things just drop for free? Is there a way I can get more?

I think you were only getting Imperial gems because you were in Whimsyshire.

There are actually two secret levels now: Whimsyshire and Whimsydale. Both are visually the same (rainbows, clouds, unicorns, etc.). You still access Whimsyshire by using the Staff of Herding in Act I. You access Whimsydale by killing a rainbow goblin in Adventure mode (he won't appear in rifts or greater rifts).

The main difference between the two zones is that in Whimsydale you get lots and lots of gems and loot, while Whimsyshire has more typical loot drops.

If you were in Whimsydale I could see that explaining the Imperial gems, but I wouldn't expect higher level gems to drop in Whimsyshire. Maybe you found a bug since most of the focus on Diablo 3 is on the level 70 end game rather than leveling up?

In any event, I wouldn't expect you to find any Imperial gems in general until you are at least level 61, as stated elsewhere.