Foamy pee in new litterbox?

We just got a new litterbox (as an addition to the one in the livingroom) and my orange boy tried it for the first time this morning. I thought he was peeing but it was taking a little longer than usual, and then I noticed he was kind of sitting in a "normal sitting" position, not the peeing position he has. After sitting for a while he got out of the box and didn't even look at his doing, he didn't hide it, he just walked away. When I checked what he left there I saw this foamy pee on top of the litter. A quick google says this could be a UTI or kidney infection, but he had a full senior panel done with urine and blood analysis just a month ago and he's in perfect health. He's behaving normally otherwise.

Any ideas if this is an urgent concern or should I just wait and see if his behaviour changes in the future?