1200-1300 Cannot Checkmate with Rook and King? Your Views

Ok, so I was playing casually with a friend of mine (1200, name him A for some simplification) some 5+1 unrated matches. We also had another friend of ours seeing the games (700, name him B for the same reasons). In one particular game, we had a position in which I had a king vs rook and king endgame, obviously losing, so I resigned. Let me tell you A had about 8 sec but the match had +1 increment so I didn't want to continue playing. After the game, friend B came up to me and said that 1200-1300 don't know how to checkmate with rook only (generally) and I would've gotten a draw. He backed up his thoughts by saying that 90% of the games get sorted out in the middlegame and only rook endgames are not common. He also said that a method should be known to checkmate with a rook (my comment: like it can't be figured out easily), he furthermore said that there is a stalemate with only rook endgames which can happen in games (Do remember he is 700 blitz in chess.com) I said that king and rook checkmate is a checkmate you should know but he is not understanding. So I decided to make this forum so that we can see that his statement is true or not.
For Clarification I'm not asking whether I should've resigned or not, I'm asking the Q. if 1200-1300 know the method (as per my friend) of checkmating with a king and rook.

I personally think only rook endgame is safer than only queen endgame, in less time, as there is no problem of stalemate  (I don't think someone rated 1200-1300 blitz would not make stalemate with rook and king).
Also, I am trying to justify my resignation was correct but he is not able to understand.

I learned it maybe 900-1000?

Anyway he should know it by now.

I learned it at 800 all my checkmated I learned without any help that’s why they are a bit sus at timed

Ok, so I can say that rook and king checkmate is easy?

Of course 1200 can do the checkmate.

But with 8 seconds (+1 increment)? I'm not so sure.

i learnt it at 400ish (lol) blitz but have never used it since maybe a 20% chance i would do it under those circumstances. you need 2 mins to do it safely(at least for me)

Ok to clarify, my friend didn't specify any time constraints and said it as a general thing.
So I take no as the answer?

Let's say I resigned because its unrated and I wouldn't have been proud or had any fun by drawing the game.

I am pretty sure, player with 1000 rating should know how to checkmate, but never give up with 8 sec left! (even with 1 sec per move bonus it is not so much time, the other player must be skilled in other case he is slow) 

Just look up at my comment, its a game between friends and its unrated. So no problem in resigning.
I resigned also due to the fact that I would've been able to checkmate in about 8 seconds, so I didn't wanted to play the game.
Also, he was trying to gain time by playing some random moves.

come on my GF could do R and K vs K on the very first day she partly learned chess.  

she could do this even before I taught her  how a knight moves.  Heck she did not even know the various ways the pawns move. 

You should test it. I'm obviously not at 1200 yet, but when I get into K vs K+R endgame, I play on for a few more steps, to see if my opponent's moves make sense. If they start out with the right moves to force a checkmate, then I resign. If they move randomly, then I have a high chance of getting a draw (or I'm giving them a chance to learn this checkmate pattern).

I'm not sure about 1200 rated players, but because of the resignations, I think that there is a high chance that many players do not actually remember these checkmate patterns all the time, simply because usually they don't have to play them out.

Players who have trouble winning with rook and king vs a lone king need someone to actually demonstrate how to do it in person.

I knew rook mate when I was  700 so easy, many people still mate u but use a wrong technique

I am 700 and I learned it at 500