I believe the solder consideration stems from the fact that when a multistranded flexible wire is soldered, at the junction where the solder stops and the strands can flex,
unless they are 100% supported they will fatigue and break at the solder/wire point -given repeated movement or vibration.
All wires, if soldered, should be mechanically stable before they are soldered.
The relay you show has posts, and the wire should be wrapped around the post before soldering.
The aim here, is that if there is excess heat -- maybe the contact burns internally, even if the solder melts the wire cant fall off.
Super X3. 3600rpm. Sheridan 6"x24" Lathe + more. Three ways to fix things: The right way, the other way, and maybe your way, which is possibly a faster wrong way.