Different circumstances in the true end.
For one Dave is more confrontational about it and in a better mental state, directly asking how Tyson felt. Dave before had been too closed off to notice what Tyson was going through, or any of his friends really.
Second Tyson's defenses are lowered from the sedatives he's recovering from. It's mentioned he's lucid, but he's also tired from driving all night to the middle of nowhere and just waking up from being knocked out. The walls he keeps between them are paper thin at that point. Also he doesn't immediately say yes, there is that brief moment you can see him try to fight it before relenting and asking how long Dave has known. Even then, he seems sad or apologetic to admit it, like he's afraid of Dave's reaction.
It's not like those are new feelings either, Tyson has loved Dave for a long while and the denial on the mountain had a fair bit to do with his self worth issues along with being a way to push Dave away to someone better. All those negative feelings haven't had a chance to fester and take hold here. Dave in return already has love for Tyson, main game he's pretty much the first of the six Dave will start to question if he's in love with, plus all the new memories he's seeing of past lives along with that encouragement from Roswell clearing things up.
Heck, special mention to Roswell's line about seeing all the different iterations of the universe, but the one thing that never changes is how much Tyson loves Dave. With Dave having his own set of memories now probably showing him the same thing.
Things on path P line up to where feelings just get acknowledged and reciprocated in a cleaner way. After all they've gone through, and how deep we know those feelings run, it feels good they get that chance to just have that happy ending together on this new prime timeline and all future iterations of the universe.