What was net difficulty in that time?
I answered this above... you even quoted it:
Target share diff was between 550K and 680K (around 10 in that other diff-format).
If you don't understand what I mean, then maybe "between 9-11" makes sense?; the hashrate/diff had been pretty steady around there, increasing a bit more now tho with the price increase (still finding the occasional block solo-mining)
I believe you are very luck, because some pool has much more hash power than you but they were not found such block in so short periods like you.
Of course luck is involved; mining is subject to huge variance. Pools tend to decrease this variance. Solo-mining is more of a gamble - it can be hugely entertaining and rewarding, or sadly disappointing. Perseverance helps. Pools often run into several blocks quickly, have gaps for a while, run into more blocks, etc... Every time I mine with a pool and add up how many blocks I found for the pool, it always seems like I should have solo-mined. Murpy's law applies here tho - you might switch to solo-mining and never hit a block; switch back to pool mining after a disappointing month of almost nothing and immediately hit 2 litecoin blocks in a row lol.