Muscle gain vs. Weight Loss

You're not asking the question "which is heavier, a pound of fat or a pound of muscle?" are you?

One way to determine muscle mass is to do a body comp test.  I use electronic calipers every morning.  If you go to a gym, they can do the test for you.  What you need to do is look at body fat percentage and see how that is changing.  I agree to avoid or discount the scale.  Some people are driven by it and don't care if they lose muscle mass.  Fat is what ya want to go. 

The answer to your question is yes. The fact that you've been working out can make your weight loss "less apparent" to the scale. It shouldn't however, be less apparent to you and how you FEEL. Given the time difference between when you were 195 and now at 205, I imagine that it's hard to qualify at which time you felt better, but i would stick to that metric rather than a number on a scale.

How your clothes fit is another good indication. Fat, being less dense than muscle, takes up more space per pound. If you've lost fat but gained muscle, you'll be smaller volumetrically even though you may not weigh any less. If your clothes are looser, that's a good indication that you've lost fat.

Yes.
It is possible to gain enough muscle mass while losing fat from training to equal out your body weight. I have experienced this myself. And since muscle does weigh significantly more than fat, a small gain in muscle can change your weight.
I am the hardest of hard gainers, and I still managed to pack on a total of 20 lbs of muscle, evident by going from 26% body fat down to 11% (for one, brief, fleeting summer) and still managing to weigh in at the same as I did while "weak & fat". My doctor and sports physiotherapist confirmed this "approx 20 lb".

In addition, the more muscle you carry, the faster your metabolism with burn, so packing on several pounds of lean muscle with rev up your fat-burning furnace and you will actually burn more calories, even at rest. Combine fat loss with the muscle gain, and your furnace is kicked up another notch, making gaining fat a little harder than being sedentary. Win - win.

Now, as for gaining significant muscle mass from doing aerobic activity like swimming, cycling, irunning, I doubt you could gain that much, (though I'm not a scientist) but it has to do with that fast twitch vs. slow twitch muscle fiber stimulation thing.
Muscle gain is maximized more through low rep resistance to absolute fatigue. This is the exact opposite of endurance sport.
It can certainly appear that you have gained muscle visually, since body fat loss will make your pecs & abs "pop out" and appear larger in proportion than you used to, but this would mean your weight would have decreased.

Just my amateur shot at it.