Yeah, as you can see, the difference between 50 yards/meters does add up over 500 meters (457 yards) but it's less than 50 yards difference, so it's not hugungous. And, if you did that twice in one day, that's awesome.

I swim with said friend that completed her first tri after not really swimming to that point, and I'm sure she would exude maximum sympathy for you swimming with someone fast in your lane or nearby. She has used the "literally swimming circles" phrase before. You may be slow relative to THEM, but think about all those people who don't even get in the pool, or people you don't see because they don't swim in the pool at the same time you do. And, it's possible those two people were a) competitive with each other, or b) swimming fast laps on purpose, which makes you seem even slower. Also, when you do kicking or pulling drills or vary your stroke, you'll feel slower, too. I, too, use these tricks myself to keep from competing with people in nearby lanes, or getting down on myself for being "slow". Almost everyone is slow compared to someone!