It makes absolute sense. This is how mining works, you get a reward only for your participation in finding a block by the pool. Last XMR block was found on May 18, the one before that was found on April 29. There is no guaranteed time it takes to find a block, only estimated, but in the end it's largely about luck. Educate yourself, use google or the FAQ over here, else you'll just making a fool of yourself. 

A mature block is one that has been confirmed by a sufficient number of subsequent blocks. For XMR I think that is 60 confirmations, so I think about 2 hours.

Read the FAQ on how PPLNS works.

It's not that easy to explain this to complete noobs, but rather than trying again, read this.

Rewards are always distributed when a block is found by the pool. It is impossible to tell you when this is expected, as the hash-rate varies, and Ethereum difficulty is on a constant rise. We found the last block 4 days ago, the one before 14 days ago, the one before 20 days ago. Judging by that, you could say that recently we land a block every 6-10days. This doesn't mean that you should expect a block to be found in the next 2-6 days, it can be found next minute, or we might even have to wait 2 weeks. The payouts go out when you reach the minimum threshold.

"the payment was also very less." The first block today had an effort of 409%. Under PPLNS model, miners are paid only for the shares that are part of the 100% effort window, all other shares get discarded. Read the FAQ and look at round 5 in the graphic. And before you ask if this is fair, yes, it is fair.

@Matthew , you only see a balance change when the pool finds blocks. See Inkies first response down here.

Like Inkie said, with the long block time windows and relevant inconsistencies, looking at profitability over a period of X hours is highly inaccurate. A more representative sample would be weeks, event 10 weeks at least.

If you are worried about profitability, don't be, it's still very profitable pretty much everywhere in the world (energy prices) and at every pool out there. On average it evens out to about same profit-abilities everywhere, assuming you are not getting stale shares, which small miners get at the big pools with no variable difficulty adjustments. You're safe here.

That's not your personal statistics, but the pools statistics showing which blocks the pool found.

Any chance you fired the miner up for couple of seconds that got you those few shares in, which was a too short period to be reflected on the graphs?