So as you go on to play this sport for a long time, you'll notice that not only do half the players not actually know the rules well, but many of them don't correctly understand the ones they DO know. So before I answer your question, just understand that you'll come across these sort of disagreements all the time. Just maintain the "spirit of the game", and be polite, plainly express your opinion about what happened, and most of the time if you both disagree, the throw will just go back to original thrower before the play happened.

Now in regards to whether you caused a strip, the only relevant explanation in the rules is here:

"Strip: If a defensive player initiates contact with the disc after an offensive player has gained possession of the disc, and the offensive player loses possession as a result, it is a strip. A strip is a subset of fouls and is treated the same way."

The key word here is "initiates." So based on this statement, it sounds like you did NOT strip the other player, but rather that he technically caught it, gained possession, and then dropped it, which would be a turnover.

Just a fair warning, this will almost NEVER end up being a turnover on the field, just because noone will ever be able to agree that you were perfectly still and that you didn't even move slightly in a way that could cause the disc to be knocked out of his hands.

You'll see similar confusion in a layout d. If the offense throws the disc and a defensive player lays out, catches it, stops rotation, and then hits the ground and drops it, its a turnover. He gained possession when he stopped rotation of the disc and caught it, and then dropped it when he hit the ground, turning it back over to the original offense. This is another one that I've seen people argue about to the end of time playing all through college and club.

In regards to your question if it was a blocking foul, I'll refer you to this part of the rules:

"When the disc is in the air a player may not move in a manner solely to prevent an opponent from taking an unoccupied path to the disc"

It seems like the difference here is whether your INTENTION was to get in his way in a manner that would obstruct his ability to get the the disc. Like if you were both chasing down a disc and you ran in front of him and intentionally stopped so that he wouldn't be able to get to the disc, then that's a blocking foul, but what you described doesn't sound like that.

Remember what I said, these rules will ALWAYS be a subject of debate so just keep a calm and positive attitude and try to talk it out. One of the best things about Ultimate is that there is always an outcome if the players agree, and if the players disagree. Not everyone is always thrilled with the outcome, but there's an outcome nonetheless.

It's good you're a new player and already looking into and asking questions about the rules. You don't need to sit down and read the whole rulebook, because most of it will come naturally as you play more, but also don't hesitate to ask your captains and experienced players whats going on in a situation you don't full understand. And you can also continue to ask these questions here, we're glad to help.