Half the KHL rinks are smaller than Olympic sized. Some of the Finnish ones are too (though not Jokerit's). And the surface you play on as a kid... they are all huge - you are not noticing a loss of time and space to shoot when you are a kid playing minor hockey on NHL vs. Olympic ice! My kids play on Olympic ice sometimes and until you get to at least older AAA level or junior ages it really makes no significant difference. The biggest factor is still the speed/strength of players the and style of play.
Smaller ice surfaces also don't shrink uniformly... the slot is still the same size, the distance from top scoring areas to the goal are still the same, and you can believe that defensemen do not choose to position themselves closer to the boards on in-zone scoring plays just because there is more space there on the outside. Where the bigger ice surface definitely does matter is for quicker players being able to skate the puck on entries. There is more space to make transition plays of all kinds really, skating or passing.
Bottom line, his coach is providing a facile answer. The AHL ice surfaces are smaller than Jokerit's, but players are also bigger, faster, and play a more aggressive style of defensive game. Tolvanen has seen plenty of smaller rinks before, both in the USHL and at home and in the KHL, though anything going back before he was 15 or 16 is absolutely inconsequential. But what he hasn't seen so much of is smaller rinks filled with the next closest thing to players with NHL size, speed, and intelligence playing an aggressive NHL-style game.
You get used to all kinds of weird rink dimensions and characteristics pretty quickly. There are some strange ones around junior rinks and probably in the AHL too though I haven't been to many AHL rinks. The old Boston Garden, Buffalo Aud or Chicago rink sizes didn't really stop Esposito or Hull from begin the best scorers in their era. But they scored a lot in tight or sniping from the slot anyway so again that's not where the main difference is felt. But if they had to go up against modern skating NHL players more often, they'd suddenly notice a reduction in time and space to get their shots off!
For what it's worth, since there's not much else going on these days.