Last difficulty increase was ~7.5%.

For that much you can attribute block discovery to be faster (in case when difficulty increases). That would be 45seconds faster.

While average time between transactions will be targeted at 10mins, times between specific blocks can vary a lot. Not long ago there was no block for 1h35mins.
And you have situations where you have 6 blocks discovered in 20mins.

It's just how statistics works.