Card Question: Sunbird's Invocation

[DoomedTraveller]

This past Friday night, I participated in a sealed event at my FLGS.  In the final round of games, I was paired with a guy who brought out the card "Sunbird's Invocation", which reads:

Sunbird's Invocation {5}{R}
Enchantment
Whenever you cast a spell from your hand, reveal the top X cards of your library, where X is that spell's converted mana cost. You may cast a card revealed this way with converted mana cost X or less without paying its mana cost. Put the rest on the bottom of your library in a random order.

The way that he played it was that when he cast his INITIAL card from his hand, he would reveal X amount of cards.  He would play a card from that reveal, but then he would reveal MORE cards after he cast the bonus card and then cast those in succession.  Under such an onslaught, I did not last long.  Unfortunately, I gave my opponent the benefit of the doubt and let this happen unchallenged (because of my relative inexperience with the game), but after mulling over what went wrong that night, I started questioning whether or not he was playing the card correctly.

My question is this - Are the cards that are being revealed by Sunbird's Invocation going into his HAND or are they being held somewhere else entirely?  If they are NOT going into his hand, then is it safe to assume that my opponent played the card incorrectly?  If these cards ARE going into his hand, then I don't understand the underlying fundamental mechanics behind this card and I need it explained.

Either way, I registered an official loss (and I learned a valuable lesson in the process), but I would like to know to make me a better player and member of the overall Magic community.

[Soren841]

Only the first one does it. The cards revealed are never put into your hand

[robort]

It is basically a cascade effect. You cast a card from your hand with say converted mana cost of 5. It doesn't have to resolve just has to be cast. You then reveal 5 cards from the top of your library and yes all 5 have to be revealed.
You may cast (lol yes 1) of those revealed cards with converted mana cost of 5 or less without paying the mana cost.
Then put the rest on the bottom of your library in random order. So you actually have to take the rest, mix them up and put them on the bottom of your library.

This also happens if you cast a card with converted mana cost of 1. You reveal 1 card from your library and if it is a card with 1 converted mana cost you may cast it without paying the cost. If it is more then 1 or a land you put it on the bottom of your library.

All cards must be revealed no matter what and must be put on the bottom of the library

[Soren841]

You only cast one

[CardAgain Sweater]

You were right and your opponent was wrong. As both robort and Soren841 have commented, the trigger is like cascade in that it digs and you can cast a spell for free.  But those cards never go 'in your hand', so sunbird's invocation does not trigger again. Unless the free spell you choose actually has the Cascade keyword (not available in standard), the chain stops with the first free spell.

[Soren841]

Speaking of which, this card is amazing with Yidris 😍

[DoomedTraveller]

Thank you for your help assisting to understand the nuances of the game better.  Next time I will be ready if such a thing happens in a game.