If you pause on the scene when Yuri is placing his credit card in the booklet, you can see he only buys one ring. For Viktor. So the ring Viktor puts on Yuri's finger wasn't planned. Viktor provided that ring.
this is the infamous receipt scene y’all are talking about:
but Yuuri also asked “Can you show me these two [rings] in front?”
unless he meant that as “show me these different two and I’ll pick the one I like more.” ??? but then Yuuri did say “This one, please. I’ll pay in installments.” that means he just bought only one ???
but later on Victor also told the group that “they’re [rings] a pair” ???
SO either ( A ) it was a major coincidence that Victor bought the same exact ring for Yuuri before Yuuri bought one or ( B ) Victor bought the matching ring right after Yuuri bought one, but the studio didn’t animate it or ( C ) Yuuri bought both rings even tho his receipt implies one ring（*・∧・*）?