How does "bitbake virtual/kernel" work if kernel recipes don't have PROVIDES variable set to virtual/kernel?

I'm trying to understand a few pieces associated with using bitbake to compile the linux image and generating a boot image that would be used to flash onto the processor.

• How come bitbake virtual/kernel really works? Read through section 2.3 and it says recipes use PROVIDES parameter to add an extra provider, which indicates a recipe could be called in multiple ways (by its name, and by whatever PROVIDES is set to). But the kernel recipes (../poky/meta-bsp/recipes-kernel) I checked didn't have PROVIDES parameter let alone it being set to virtual/kernel.
• Upon running bitbake virtual/kernel, how come a boot.img is being generated when it should only just be generating a linux binary i.e vmlinux for instance?In one of the kernel .inc files, I see:

DEPENDS += " mkbootimg-native openssl-native kern-tools-native"...FILESPATH =+"${WORKSPACE}:"SRC_URI   =  "file://kernel \              ${@bb.utils.contains('DISTRO_FEATURES', 'systemd', 'file://systemd.cfg', '', d)} \              ${@bb.utils.contains('DISTRO_FEATURES', 'virtualization', 'file://virtualization.cfg', '', d)} \              ${@bb.utils.contains('DISTRO_FEATURES', 'nand-squashfs', 'file://squashfs.cfg', '', d)} \

mkbootimg-native I reckon refers to the boot image recipe that the kernel recipe depends on, though shouldn't it be the other way around since the boot image should contain the kernel image itself?

• lastly, is there a way to put debug prints in different recipe files to see if it's being invoked? I tried echo...to no avail