It's like this:
It absolutely true that Rios was a much better offensive player in July than Infante. There's literally no stat you can look at to say otherwise, unless you're looking at it incorrectly.
5 hits over a month is the difference between a guy who hits .300 and a guy who hits .240. That's 30 hits over the course of a year. That is a significant difference. (And hits are an antiquated way to evaluate a player, anyway).
Omar Infante posted a sub-.600 OPS in July, just like he has in every month except April (when he put up a whopping .621).
Alex Rios posted a .736 in July. I don't think that's a great month, but that type of performance would create a significant increase in offensive production over a sample size of a few months or a full season, when compared with who Infante was then and of late.
150 points of OPS difference is a significant improvement. That
IS "trending so much better."
They're both going to play a lot between now and when Gordon returns. If Rios continues to produce at the solid, slightly above average rate he did in July, he should continue to play. If he slides back and his production looks more like the aggregate of his season, then Infante should play due to his defensive value.