That is true no hoses are seen between the two ships. So if not transferring fuel to the cruiser, perhaps a crew or mail transfer. The Shiretoko class would not have carried much in the way of other stores to transfer to another ship. They were primarily fleet oilers. However, the pic does show the IJN had developed the required seamanship to maneuver two large ships in a position that refueling could have taken place.

This article may provide some additional light on the subject although the author does not identify his sources.

https://thediplomat.com/2020/01/were-tankers-the-key-to-imperial-japans-early-wartime-success/

I will continue looking but other than the picture of a Tone class cruiser being refueled alongside a tanker in 1944 that may be the only definitive proof we have of side by side replenishment by the IJN.
https://www.pinterest.jp/pin/770537817470888349/