Need Help With A Silver Dollar

Over the weekend, I had an odd opportunity arise. I was at one of my pick up banks, and as I was finishing with the teller, a gentleman came in and approached the other teller and said he wanted to cash in some coins. (both tellers are aware I am a coin collector). The man being boisterous said that he had tried to cash them at a few banks and none would do it.

I said I would be interested, so he came over and put down the coins, and the first things I looked at were a few nickel half dollars. they did not look or really feel right to me.

then I looked at his dollars he had.

3 were dated 1971, however I had never seen the design, I would have expected to see a voyager, however they were all the BC coat of arms.
As I was not expecting this, I thought these were some sort of Trade dollar.

The last 2 I was familiar with, however they looked unnaturally shinny. They were (I am sorry I don't remember the correct name or term) but I believe they were sold at the mint as souvenirs. Dollar sized coin with the RCM logo on it.

I decided to pass on the coins, mainly because of 2 things, the look and feel of the 50 cent pieces (but hindsight, who would fake one?) and the vibe I got from the guy.

So onto the next bank I went, and I kept replaying the whole thing in my head, something was not adding up. I googled the 71 coin, and the first thing I saw was the dang 50% silver BC coin (man I was stupid)

Then I remembered that someone (probably SPP-Ottawa) mentioned that this coin was actually produced in Nickel, Silver or Platinum(?)

(I tried searching for the thread to no avail)

So you guessed it, I turned around and went back.

I got there, and the tellers were surprised to see me back, I asked if they bought the coins, and if I could buy them.

The one teller said that she had first dibs, because I passed on them already and she took the 2 RCM medallions.

I bought the 3 BC silver dollars.

All that to ask this, Am I correct that that coin was a souvenir from the mint and not an actual "silver dollar"?

on the back of the coin it does say dollar.

secondly, was I also correct in remembering the coin was made in Platinum as well as silver?

lastly if yes, then how can you tell the difference? is Platinum non-magnetic? is there a significant weight difference?

I would imagine this coin in Platinum would be significantly more valuable, what are the silver/platinum worth (or how much did I loose out on?)

Thanks for the information.