No, the origin city will siphon production towards anything the target city builds.
- units will have hammers added to their progress, even if you can’t build them yourself. Note that unique units are counted separately from base units, so if you sent a TR to an Aztec city that built a Jaguar then it wouldn’t contribute to a warrior in your city. But it would contribute to getting a Jaguar in your city if you got enough free siphon
- buildings and wonders have their production siphoned, but only if you don’t already have the building.
- projects and processes in cities are siphoned as you would expect